[web] Add admin permission `create-subscription` (#27382)

* Add capability `create-subscription`

* Check `create-subscription` (frontend)

* Check `create-subscription` (backend)

* Update tests

GitOrigin-RevId: bc75b99f74573f50d5b1cb003244658040c76064

services/web/types/admin-capabilities.ts

@@ -1,6 +1,7 @@
 export type AdminCapability =
   | 'clear-saml-data'
   | 'clear-session'
+  | 'create-subscription'
   | 'modify-login-status'
   | 'modify-user-email'
   | 'modify-user-name'