Add memcache support for admin bucket in helm

[lamida]

What this PR does

Add admin-cache component to cache admin bucket in GEM.

Which issue(s) this PR fixes or relates to

Fixes #3744

This PR depends on https://github.com/grafana/backend-enterprise/pull/4084

Checklist

• [ ] Tests updated
• [ ] Documentation added
• [x] CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

[ortuman]

As a reminder, don't forget to add admin client cache specific parameters to the admin_client section in the values.yaml file to make it point to this new component.

These are not yet available, but they will as soon as https://github.com/grafana/backend-enterprise/pull/4030 gets merged into master.

This could be done here or in a follow-up PR.

[lamida]

@dimitarvdimitrov the PR was not ready yesterday because I was doing some testing and needed to do some refactoring. I haven't 100% testing the last updated changes again but feel free to quick review first. Changes from last review (before yesterday):

• Use backend key for cache type
• Remove redis reference from all helm manifest

I might still missing something, I will revisit again tomorrow but feel free to do a quick skim first.

Please check this PR https://github.com/grafana/backend-enterprise/pull/4084 too to allow using backend for cache type.

[56quarters]

The CHANGELOG has just been cut to prepare for the next Mimir release. Please rebase main and eventually move the CHANGELOG entry added / updated in this PR to the top of the CHANGELOG document. Thanks!

[lamida]

@dimitarvdimitrov please help to review this PR again when you are free.