Add `branch_type` support to scan result policies

What does this MR do and why?

We are adding branch_type support to security policies (&9468 (closed)).

This MR adds branch_type support to Scan result policies.

How to set up and validate locally

• Create a new group

• Create a new contained project

• Enable the feature flag for the project:

  Feature.enable(:security_policies_branch_type, Project.last)

• Navigate to Repository > Branches and create the following branches:

  • develop
  • feature-1

• Navigate to Settings > Repository and protect the develop branch

• Navigate to Settings > Repository and within the Branch defaults section, set develop as default branch

• On the group level, navigate to Security and Compliance > Policies and create the following scan result policy:

  type: scan_result_policy
  name: Container Scanning Default Branch
  description: ''
  enabled: true
  rules:
  - type: scan_finding
    branch_type: default
    scanners:
    - container_scanning
    vulnerabilities_allowed: 0
    severity_levels: []
    vulnerability_states: []
  actions:
  - type: require_approval
    approvals_required: 1
    user_approvers_ids:
    - 1

• On the project level, navigate to Security and Compliance > Policies and create the following scan result policy:

  type: scan_result_policy
  name: Secret Detection Protected Branches
  description: ''
  enabled: true
  rules:
  - type: scan_finding
    branch_type: protected
    scanners:
    - secret_detection
    vulnerabilities_allowed: 0
    severity_levels: []
    vulnerability_states: []
  actions:
  - type: require_approval
    approvals_required: 1
    user_approvers_ids:
    - 1

• Open MRs targeting the following branches and verify the expected approval rules:

  Target branch	Approval rules
  main	Secret Detection Protected Branches
  develop	Secret Detection Protected Branches , Container Scanning Default Branch
  feature-1	none

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 #404785 (closed)