[web] Add admin permission `modify-feature-override` (#27395)

* Add capability `modify-feature-overrides`

* Check `modify-feature-overrides` for create endpoint (frontend)

* Check `modify-feature-overrides` for create endpoint (backend)

* Update tests

* Check `modify-feature-override` for delete endpoint (frontend)

* Check `modify-feature-override` for delete endpoint (backend)

* Update tests

* Fixup test name

Co-authored-by: Andrew Rumble <andrew.rumble@overleaf.com>

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Co-authored-by: Andrew Rumble <andrew.rumble@overleaf.com>
GitOrigin-RevId: ebf37e48fed1dd6fda23ca8c7a5baf55af1cde38

services/web/types/admin-capabilities.ts

@@ -3,6 +3,7 @@ export type AdminCapability =
   | 'clear-session'
   | 'create-recurly-account'
   | 'create-subscription'
+  | 'modify-feature-override'
   | 'modify-login-status'
   | 'modify-user-email'
   | 'modify-user-name'