Implement an in-process distributed cache to avoid the need to use an external cache server like memcached

[dannykopping]

Is your feature request related to a problem? Please describe.
It is sometimes not desirable or even possible for users to run Loki with a cluster of memcached/redis instances for Loki's 3 caches (chunk, index query, result) to improve performance.

Describe the solution you'd like
Implement an in-process distributed cache. Groupcache is a great option here as it's written in Go (:heavy_check_mark:) by the legendary Brad Fitzpatrick who wrote memcached (:heavy_check_mark:).

Describe alternatives you've considered
Add a ring to our existing fifocache

Additional context
There is a fork available which adds some extra features.

[liguozhong]

That's a great idea，It's really difficult to operate a cache system. I really agree to use loki memory for cache module.

[stale]

Hi! This issue has been automatically marked as stale because it has not had any
activity in the past 30 days.

We use a stalebot among other tools to help manage the state of issues in this project.
A stalebot can be very useful in closing issues in a number of cases; the most common
is closing issues or PRs where the original reporter has not responded.

Stalebots are also emotionless and cruel and can close issues which are still very relevant.

If this issue is important to you, please add a comment to keep it open. More importantly, please add a thumbs-up to the original issue entry.

We regularly sort for closed issues which have a stale label sorted by thumbs up.

We may also:

• Mark issues as revivable if we think it's a valid issue but isn't something we are likely
  to prioritize in the future (the issue will still remain closed).
• Add a keepalive label to silence the stalebot if the issue is very common/popular/important.

We are doing our best to respond, organize, and prioritize all issues but it can be a challenging task,
our sincere apologies if you find yourself at the mercy of the stalebot.