Fix cross database join in fetch_policy_approvers_service

What does this MR do and why?

This fixes a cross database join between users and members by splitting the query up in two queries

Database

1st Query `container.authorizable_members_with_parents.pluck(:user_id)`

Query plan

SELECT 
  "members"."user_id" 
FROM 
  (
    (
      SELECT 
        "members"."id", 
        "members"."access_level", 
        "members"."source_id", 
        "members"."source_type", 
        "members"."user_id", 
        "members"."notification_level", 
        "members"."type", 
        "members"."created_at", 
        "members"."updated_at", 
        "members"."created_by_id", 
        "members"."invite_email", 
        "members"."invite_token", 
        "members"."invite_accepted_at", 
        "members"."requested_at", 
        "members"."expires_at", 
        "members"."ldap", 
        "members"."override", 
        "members"."state", 
        "members"."invite_email_success", 
        "members"."member_namespace_id", 
        "members"."member_role_id", 
        "members"."expiry_notified_at" 
      FROM 
        "members" 
      WHERE 
        "members"."type" = 'GroupMember' 
        AND "members"."source_type" = 'Namespace' 
        AND "members"."source_id" = 9970
    ) 
    UNION 
      (
        WITH "group_group_links_cte" AS MATERIALIZED (
          SELECT 
            "group_group_links".* 
          FROM 
            "group_group_links" 
          WHERE 
            "group_group_links"."shared_group_id" = 9970
        ) 
        SELECT 
          "members"."id", 
          LEAST(
            "group_group_links"."group_access", 
            "members"."access_level"
          ) AS access_level, 
          "members"."source_id", 
          "members"."source_type", 
          "members"."user_id", 
          "members"."notification_level", 
          "members"."type", 
          "members"."created_at", 
          "members"."updated_at", 
          "members"."created_by_id", 
          "members"."invite_email", 
          "members"."invite_token", 
          "members"."invite_accepted_at", 
          "members"."requested_at", 
          "members"."expires_at", 
          "members"."ldap", 
          "members"."override", 
          "members"."state", 
          "members"."invite_email_success", 
          "members"."member_namespace_id", 
          "members"."member_role_id", 
          "members"."expiry_notified_at" 
        FROM 
          "members", 
          "group_group_links_cte" AS "group_group_links" 
        WHERE 
          "members"."type" = 'GroupMember' 
          AND "members"."source_type" = 'Namespace' 
          AND "members"."requested_at" IS NULL 
          AND "members"."source_id" = "group_group_links"."shared_with_group_id" 
          AND "members"."source_type" = 'Namespace' 
          AND "members"."state" = 0 
          AND (members.access_level > 5)
      )
  ) members 
WHERE 
  "members"."type" = 'GroupMember' 
  AND "members"."source_type" = 'Namespace' 
  AND "members"."user_id" IS NOT NULL 
  AND "members"."state" = 0 
  AND "members"."requested_at" IS NULL 
  AND (members.access_level > 5)

2nd Query `User.by_ids_or_usernames(user_ids, user_names).where(id: ...)`

Query plan

SELECT 
  "users"."id", 
  "users"."email", 
  "users"."encrypted_password", 
  "users"."reset_password_token", 
  "users"."reset_password_sent_at", 
  "users"."remember_created_at", 
  "users"."sign_in_count", 
  "users"."current_sign_in_at", 
  "users"."last_sign_in_at", 
  "users"."current_sign_in_ip", 
  "users"."last_sign_in_ip", 
  "users"."created_at", 
  "users"."updated_at", 
  "users"."name", 
  "users"."admin", 
  "users"."projects_limit", 
  "users"."failed_attempts", 
  "users"."locked_at", 
  "users"."username", 
  "users"."can_create_group", 
  "users"."can_create_team", 
  "users"."state", 
  "users"."color_scheme_id", 
  "users"."password_expires_at", 
  "users"."created_by_id", 
  "users"."last_credential_check_at", 
  "users"."avatar", 
  "users"."confirmation_token", 
  "users"."confirmed_at", 
  "users"."confirmation_sent_at", 
  "users"."unconfirmed_email", 
  "users"."hide_no_ssh_key", 
  "users"."admin_email_unsubscribed_at", 
  "users"."notification_email", 
  "users"."hide_no_password", 
  "users"."password_automatically_set", 
  "users"."encrypted_otp_secret", 
  "users"."encrypted_otp_secret_iv", 
  "users"."encrypted_otp_secret_salt", 
  "users"."otp_required_for_login", 
  "users"."otp_backup_codes", 
  "users"."public_email", 
  "users"."dashboard", 
  "users"."project_view", 
  "users"."consumed_timestep", 
  "users"."layout", 
  "users"."hide_project_limit", 
  "users"."note", 
  "users"."unlock_token", 
  "users"."otp_grace_period_started_at", 
  "users"."external", 
  "users"."incoming_email_token", 
  "users"."auditor", 
  "users"."require_two_factor_authentication_from_group", 
  "users"."two_factor_grace_period", 
  "users"."last_activity_on", 
  "users"."notified_of_own_activity", 
  "users"."preferred_language", 
  "users"."theme_id", 
  "users"."accepted_term_id", 
  "users"."feed_token", 
  "users"."private_profile", 
  "users"."roadmap_layout", 
  "users"."include_private_contributions", 
  "users"."commit_email", 
  "users"."group_view", 
  "users"."managing_group_id", 
  "users"."first_name", 
  "users"."last_name", 
  "users"."static_object_token", 
  "users"."role", 
  "users"."user_type", 
  "users"."static_object_token_encrypted", 
  "users"."otp_secret_expires_at", 
  "users"."onboarding_in_progress" 
FROM 
  "users" 
WHERE 
  (
    "users"."username" = 'Andysoiron' 
    OR "users"."id" = 16943
  ) 
  AND "users"."id" = 16943

How to set up and validate locally

Copied from !113114 (merged)

1. Create a new group
2. Add members to the group and note their IDs
3. Create a project within the group
4. Add a scan result policy to the project that lists the user IDs as user_approvers, e.g.:

type: scan_result_policy
name: foobar
description: ''
enabled: true
rules:
  - type: license_finding
    branches: []
    match_on_inclusion: true
    license_types:
      - MIT License
    license_states:
      - newly_detected
actions:
  - type: require_approval
    approvals_required: 1
    user_approvers_ids:
      - 16
      - 14
      - 15

5. Navigate to the policy list, click on the newly created policy and verify the sidebar drawer correctly lists the users.
6. Click "Edit policy" and verify the approver list correctly lists the users.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #417460 (closed)