Synchronize indexes (`idx_approval_mr_rules_on_config_id_and_id`, `idx_merge_requests_on_unmerged_state_id`)

Why are we doing this work?

We need to synchronously create the indexes that were scheduled for creation in !143668 (merged).

See: !143668 (comment 1776634559)

Implementation Plan

class AddIndexApprovalMergeRequestRulesOnConfigIdAndIdAndUpdatedAt < Gitlab::Database::Migration[2.2]
  milestone '16.10'

  disable_ddl_transaction!

  INDEX_NAME = :idx_approval_mr_rules_on_config_id_and_id_and_updated_at
  TABLE_NAME = :approval_merge_request_rules

  def up
    add_concurrent_index(TABLE_NAME, %i[security_orchestration_policy_configuration_id id updated_at], name: INDEX_NAME)
  end

  def down
    remove_concurrent_index_by_name(TABLE_NAME, INDEX_NAME)
  end
end

class AddIndexMergeRequestsOnUnmergedStateId < Gitlab::Database::Migration[2.2]
  milestone '16.10'

  disable_ddl_transaction!

  INDEX_NAME = :idx_merge_requests_on_unmerged_state_id
  TABLE_NAME = :merge_requests

  def up
    add_concurrent_index(TABLE_NAME, :id, name: INDEX_NAME, where: "state_id <> 3")
  end

  def down
    remove_concurrent_index_by_name(TABLE_NAME, INDEX_NAME)
  end
end

class RemoveIndexApprovalMergeRequestRulesOnSecOrchestrationConfigId < Gitlab::Database::Migration[2.2]
  milestone '16.10'

  disable_ddl_transaction!

  TABLE_NAME = :approval_merge_request_rules
  INDEX_NAME = :idx_approval_merge_request_rules_on_sec_orchestration_config_id

  def up
    remove_concurrent_index_by_name(TABLE_NAME, INDEX_NAME)
  end

  def down
    add_concurrent_index(TABLE_NAME, :security_orchestration_policy_configuration_id, name: INDEX_NAME)
  end
end