Mark pages as belonging to Database group

I think these pages probably belong to a database-related group,
probably Database itself.

doc/development/background_migrations.md

 ---
-type: reference, dev
-stage: none
-group: Development
-info: "See the Technical Writers assigned to Development Guidelines: https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments-to-development-guidelines"
+stage: Enablement
+group: Database
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
 ---
 
 # Background migrations

doc/development/cached_queries.md

 ---
-stage: none
-group: unassigned
+stage: Enablement
+group: Memory
 info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
 ---
 

doc/development/database/client_side_connection_pool.md

 ---
-type: dev, reference
-stage: none
-group: Development
-info: "See the Technical Writers assigned to Development Guidelines: https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments-to-development-guidelines"
+stage: Enablement
+group: Database
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
 ---
 
 # Client-side connection-pool

doc/development/deleting_migrations.md

 ---
-stage: none
-group: unassigned
+stage: Enablement
+group: Database
 info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
 ---
 

doc/development/post_deployment_migrations.md

 ---
-stage: none
-group: unassigned
+stage: Enablement
+group: Database
 info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
 ---
 

doc/development/query_recorder.md

 ---
-stage: none
-group: unassigned
+stage: Enablement
+group: Database
 info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
 ---
 

doc/development/single_table_inheritance.md

 ---
-stage: none
-group: unassigned
+stage: Enablement
+group: Database
 info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
 ---