Loki: Implement Cortex readiness Handler in Loki

[adityacs]

**Is your feature request related to a problem?
Loki currently handles /ready endpoint individually for each modules. Also, we are missing /ready endpoint for query-frontend.

Describe the solution you'd like
Cortex now has readiness Handler irrespective of module. Loki should implement this

[cyriltovena]

I'm going to assign this to Peter ! I think he has plan for this.

[adityacs]

@cyriltovena Sure.
@pstibrany I have changed the title and description of this issue

[pstibrany]

https://github.com/grafana/loki/pull/1804 implements unified /ready handler (among other things) that works in microservices as well as single-binary mode.

[stale[bot]]

This issue has been automatically marked as stale because it has not had any activity in the past 30 days. It will be closed in 7 days if no further activity occurs. Thank you for your contributions.

[adityacs]

@cyriltovena We can close this issue as #1804 is merged.