Assign database.pg_system_id metric to Enablement

config/metrics/counts_all/20210216183248_pg_system_id.yml

 ---
 key_path: database.pg_system_id
-description: ''
-product_section: ''
-product_stage: ''
-product_group: ''
-product_category: ''
+description: TBD
+product_section: enablement
+product_stage: enablement
+product_group: group::distribution
+product_category:
 value_type: number
 status: data_available
 time_frame: all

doc/development/usage_ping/dictionary.md

@@ -6350,7 +6350,7 @@ Missing description
 
 [YAML definition](https://gitlab.com/gitlab-org/gitlab/-/blob/master/config/metrics/counts_all/20210216183248_pg_system_id.yml)
 
-Group: ``
+Group: `group::distribution`
 
 Status: `data_available`