Update gitlab:db:configure for multiple databases

Update the configure rake task to work when multiple databases are
configured. The behavior should remain the same if only one database is
configured (or one database with database_tasks are enabled).

lib/tasks/gitlab/db.rake

@@ -84,16 +84,38 @@ namespace :gitlab do
 
     desc 'GitLab | DB | Configures the database by running migrate, or by loading the schema and seeding if needed'
     task configure: :environment do
-      # Check if we have existing db tables
-      # The schema_migrations table will still exist if drop_tables was called
-      if ActiveRecord::Base.connection.tables.count > 1
-        Rake::Task['db:migrate'].invoke
+      databases_with_tasks = ActiveRecord::Base.configurations.configs_for(env_name: Rails.env)
+
+      databases_loaded = []
+
+      if databases_with_tasks.size == 1
+        next unless databases_with_tasks.first.name == 'main'
+
+        connection = Gitlab::Database.database_base_models['main'].connection
+        databases_loaded << configure_database(connection)
       else
-        # Add post-migrate paths to ensure we mark all migrations as up
+        Gitlab::Database.database_base_models.each do |name, model|
+          next unless databases_with_tasks.any? { |db_with_tasks| db_with_tasks.name == name }
+
+          databases_loaded << configure_database(model.connection, database_name: name)
+        end
+      end
+
+      Rake::Task['db:seed_fu'].invoke if databases_loaded.present? && databases_loaded.all?
+    end
+
+    def configure_database(connection, database_name: nil)
+      database_name = ":#{database_name}" if database_name
+      load_database = connection.tables.count <= 1
+
+      if load_database
         Gitlab::Database.add_post_migrate_path_to_rails(force: true)
-        Rake::Task['db:structure:load'].invoke
-        Rake::Task['db:seed_fu'].invoke
+        Rake::Task["db:schema:load#{database_name}"].invoke
+      else
+        Rake::Task["db:migrate#{database_name}"].invoke
       end
+
+      load_database
     end
 
     desc 'GitLab | DB | Run database migrations and print `unattended_migrations_completed` if action taken'