Suggest issues when typing title

What does this MR do?

Suggests possibly related issues to the user when they are typing the title.

note This uses GraphQL which is behind a feature flag, to enable run bundle exec rails r 'Feature.enable(:graphql)'

note This is behind a feature flag, to enable run bundle exec rails r 'Feature.enable(:issue_suggestions)'

What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/22071

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• 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.