[CE] Improve `wait_for_push`

What does this MR do?

Uses the Events API to wait for pushes to be completed.

Makes Resource::Repository::ProjectPush wait for push by default so most tests don't need to call it.

EE MR: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/8986

What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/53308

Does this MR meet the acceptance criteria?

• [-] Changelog entry added, if necessary
• [-] Documentation created/updated
• Tests added for this feature/bug
• [-] Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• [-] Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• [-] Security reports checked/validated by reviewer