Make CI status in dashboard behind a feature flag

What does this MR do?

Makes the pipeline status in the dashboard projects and explore projects pages behind a feature flag.

This is so that we can try to disable it and see if it is really needed.

This should reduce the Gitaly calls for these pages to 0.

We're doing this because it's bad for these pages to be slow because the projects dashboard is the default home page for signed in users. And on GitLab.com we're seeing that the p95 latency for this page is 15 seconds and this is due to the Gitaly calls it makes when those Gitaly nodes are under high load.

Testing locally

1. Disable the feature flag: Feature.disable(:dashboard_pipeline_status)
2. You should see that there are no more pipeline status icons in http://localhost:3000/dashboard/projects, http://localhost:3000/explore, and the tabs under those
3. You should also see 0 Gitaly calls in the performance bar

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• 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

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

#20190 (closed) #37953 (closed)