Move external_pull_requests to CI DB

This feature is tightly linked to CI as it's only useful for CI
pipelines running against external pull requests so it makes sense to
move it to the `ci` database.

app/models/external_pull_request.rb

@@ -11,7 +11,7 @@
 # When the mirror is updated and changes are pushed to branches we check
 # if there are open pull requests for the source and target branch.
 # If so, we create pipelines for external pull requests.
-class ExternalPullRequest < ApplicationRecord
+class ExternalPullRequest < Ci::ApplicationRecord
   include Gitlab::Utils::StrongMemoize
   include ShaAttribute
 
@@ -40,6 +40,9 @@ class ExternalPullRequest < ApplicationRecord
   scope :by_source_branch, ->(branch) { where(source_branch: branch) }
   scope :by_source_repository, -> (repository) { where(source_repository: repository) }
 
+  # Needed to override Ci::ApplicationRecord as this does not have ci_ table prefix
+  self.table_name = 'external_pull_requests'
+
   def self.create_or_update_from_params(params)
     find_params = params.slice(:project_id, :source_branch, :target_branch)
 

lib/gitlab/database/gitlab_schemas.yml

@@ -200,7 +200,7 @@ experiment_subjects: :gitlab_main
 experiment_users: :gitlab_main
 external_approval_rules: :gitlab_main
 external_approval_rules_protected_branches: :gitlab_main
-external_pull_requests: :gitlab_main
+external_pull_requests: :gitlab_ci
 external_status_checks: :gitlab_main
 external_status_checks_protected_branches: :gitlab_main
 feature_gates: :gitlab_main