Merge branch 'amandarueda-master-patch-35497' into 'master'

Updating metric category to Subscription from Optional

See merge request gitlab-org/gitlab!74241

ee/config/metrics/license/20210531204603_license_billable_users.yml

 ---
-data_category: optional
+data_category: subscription
 key_path: license_billable_users
 name: billable_users
 description: Number of all billable users (active users excluding bots and guests).