Backport `database_tasks:` from Rails 7.x

For some configurations of databases we should skip
creating, dropping or running migrations.

In particular this applies to Phase 4, where we should
not create, drop or migrate the `ci:` if it points to
the same database as `main:`.

This is well supported in Rails 7. This backports exact
same config to achieve exactly the same outcome.

Rakefile

@@ -11,6 +11,8 @@ require File.expand_path('config/application', __dir__)
 relative_url_conf = File.expand_path('config/initializers/relative_url', __dir__)
 require relative_url_conf if File.exist?("#{relative_url_conf}.rb")
 
+require File.expand_path('config/initializers/01_active_record_database_tasks_configuration_flag.rb', __dir__)
+
 Gitlab::Application.load_tasks
 
 Knapsack.load_tasks if defined?(Knapsack)

config/initializers/01_active_record_database_tasks_configuration_flag.rb

+# frozen_string_literal: true
+
+if Rails::VERSION::MAJOR >= 7
+  raise "Remove `#{__FILE__}`. This is backport of `database_tasks:` Rails 7.x feature."
+end
+
+# This backports `database_tasks:` feature to skip running migrations for some databases
+# PR: https://github.com/rails/rails/pull/42794/files
+
+module DatabaseTasks
+  module ActiveRecordDatabaseConfigurations
+    def configs_for(env_name: nil, name: nil, include_replicas: false)
+      configs = super
+
+      unless include_replicas
+        if name
+          configs = nil unless configs&.database_tasks?
+        else
+          configs = configs.select do |db_config|
+            db_config.database_tasks?
+          end
+        end
+      end
+
+      configs
+    end
+  end
+
+  module ActiveRecordDatabaseConfigurationsHashConfig
+    def database_tasks? # :nodoc:
+      !replica? && !!configuration_hash.fetch(:database_tasks, true)
+    end
+  end
+end
+
+ActiveRecord::DatabaseConfigurations.prepend(DatabaseTasks::ActiveRecordDatabaseConfigurations)
+ActiveRecord::DatabaseConfigurations::HashConfig.prepend(DatabaseTasks::ActiveRecordDatabaseConfigurationsHashConfig)