- This MR is preparation (pre-work) for a feature similar to
  the Protected badge in the context of "Protected packages":
  - https://gitlab.com/gitlab-org/gitlab/-/issues/467718
  - https://gitlab.com/gitlab-org/gitlab/-/issues/441346

- When working on a similar feature in the context of
  "Protected packages", it was necessary to add
  a new GraphQL field "protectionRuleExists" to determine
  if a protection rule exists for a given package,
  see https://gitlab.com/gitlab-org/gitlab/-/merge_requests/146206 and
  https://gitlab.com/gitlab-org/gitlab/-/merge_requests/141134

- This MR focusses on adding this a new GraphQL
  field "protectionRuleExists" to the container repository type
  that can be consumed in upcoming MRs

Changelog: added