Fix more N+1 issues when indexing notes in Elasticsearch

What does this MR do?

Since we already had an N+1 test this required a couple of changes to detect these problems:

1. Add :elastic to the test setup in order to allow for GitLab to finish setting up the Elasticsearch index and ensure that the remove_permissions_data_from_notes_documents was considered finished. Without this we couldn't trigger the logic to load project permissions for the notes https://gitlab.com/gitlab-org/gitlab/-/blob/02f78e50879aa2e9facafe724a61e20d4640a342/ee/lib/elastic/latest/note_instance_proxy.rb#L33
2. We also needed to move a stub_const into a separate test block so it didn't interfere with the N+1 test for notes. Without this we weren't actually processing all the notes and the test was a false positive. The stub_const here was only necessary for the one test that actually tests this limit. It was actually interfering with some other N+1 tests where we were adding more than 10 documents. As such moving this closer to the relevant test makes more sense. It also required updating a few of the other tests to stop referring to the limit variable. This value was always equal to the number of documents in fake_refs anyway so it was unnecessary to have this variable.

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
  • I have not included a changelog entry because _____.
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Related to #324745 (closed)