Add an option to hide certain users in the UI (#28942)

* Add an option to hide certain users in the UI

* revert changes for admin users routes

* fix sqlstore function name

* Improve slice management

Co-authored-by: Emil Tullstedt <emil.tullstedt@grafana.com>

* Hidden users: convert slice to map

* filter with user logins instead of IDs

* put HiddenUsers in Cfg struct

* hide hidden users from dashboards/folders permissions list

* Update conf/defaults.ini

Co-authored-by: Torkel Ödegaard <torkel@grafana.com>

* fix params order

* fix tests

* fix dashboard/folder update with hidden user

* add team tests

* add dashboard and folder permissions tests

* fixes after merge

* fix tests

* API: add test for org users endpoints

* update hidden users management for dashboard / folder permissions

* improve dashboard / folder permissions tests

* fixes after merge

* Guardian: add hidden acl tests

* API: add team members tests

* fix team sql syntax for postgres

* api tests update

* fix linter error

* fix tests errors after merge

Co-authored-by: Emil Tullstedt <emil.tullstedt@grafana.com>
Co-authored-by: Torkel Ödegaard <torkel@grafana.com>
Co-authored-by: Leonard Gram <leo@xlson.com>

conf/sample.ini

@@ -295,6 +295,9 @@
 # The duration in time a user invitation remains valid before expiring. This setting should be expressed as a duration. Examples: 6h (hours), 2d (days), 1w (week). Default is 24h (24 hours). The minimum supported duration is 15m (15 minutes).
 ;user_invite_max_lifetime_duration = 24h
 
+# Enter a comma-separated list of users login to hide them in the Grafana UI. These users are shown to Grafana admins and themselves.
+; hidden_users = 
+
 [auth]
 # Login cookie name
 ;login_cookie_name = grafana_session