User limit enforcement (#26511)

* Added hard limits when creating user

* Added check to user activation

* Added missing check for licensed servers

* Fix i18n

* Fixed style order

* Added a separate hard limit along with existing 10k user soft limit

* For CI

* Fixing flaky test, hopefully

* Added tests

server/i18n/en.json

@@ -4178,6 +4178,10 @@
     "id": "api.user.create_user.signup_link_invalid.app_error",
     "translation": "The signup link does not appear to be valid."
   },
+  {
+    "id": "api.user.create_user.user_limits.exceeded",
+    "translation": "Can't create user. Server exceeds safe user limit. Contact your system administrator."
+  },
   {
     "id": "api.user.delete_channel.not_enabled.app_error",
     "translation": "Permanent channel deletion feature is not enabled. Please contact your System Administrator."
@@ -7178,6 +7182,10 @@
     "id": "app.user.update.finding.app_error",
     "translation": "We encountered an error finding the account."
   },
+  {
+    "id": "app.user.update_active.user_limit.exceeded",
+    "translation": "Can't activate user. Server exceeds safe user limit. Contact your system administrator. Error code: ERROR_SAFETY_LIMITS_EXCEEDED."
+  },
   {
     "id": "app.user.update_active_for_multiple_users.updating.app_error",
     "translation": "Unable to deactivate guests."