Error tracking reactive cache

What does this MR do?

This adds on top of https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/24188 the ReactiveCache. What does it mean?

The list of sentry issues will not be immediately available, rather:

1. API endpoint when requesting for the first time will return 204,
2. API endpoint when data is available will return a json.
3. The frontend should retry fetching the data using new Poll class on frontend

What are the relevant issue numbers?

Related to: #55178 (closed)

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