Add metadata info

Update pages with metadata info.

doc/update/mysql_to_postgresql.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/update/patch_versions.md

 ---
-stage: none
-group: unassigned
+stage: Enablement
+group: Distribution
 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
 comments: false
 ---

doc/update/restore_after_failure.md

 ---
-stage: none
-group: unassigned
+stage: Enablement
+group: Distribution
 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/update/upgrading_from_ce_to_ee.md

 ---
-stage: none
-group: unassigned
+stage: Enablement
+group: Distribution
 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
 comments: false
 ---

doc/update/upgrading_from_source.md

 ---
-stage: none
-group: unassigned
+stage: Enablement
+group: Distribution
 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
 comments: false
 ---

doc/update/upgrading_postgresql_using_slony.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
 ---