Improve `/-/health` to look at state of master

What does this MR do?

1. This moves blackout period to shutdown: blackout_seconds:,
2. This moves a blackout period logic to LifecycleEvents,
3. This makes web_exporter to use lifecycle events for blackout period,
4. This adds additional health check to look at state of master process
5. This health check is exposed in /-/liveness|readiness,
6. Move all existing checks under ?all=true for /-/readiness
7. This deprecates health-checks on web_exporter endpoint
8. Exempt /liveness and /readiness from Rack Attack
9. Make /liveness and /readiness to not hit DB/Redis
10. Optimise Rack Attack handling

Related

#35343 (closed)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• 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