Fixed panic when Mimir is running in single binary mode and results cache is enabled

[pracucci]

What this PR does

We add component label to all memcached clients, except the results cache. This makes memcached client metrics clash when running in single binary mode and results cache is enabled, leading to a panic. This PR fixes it.

Which issue(s) this PR fixes or relates to

Fixes #1698

Checklist

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

[replay]

If all other instances of the results cache have the component label in their metrics, why do the query-frontend results cache metrics clash with any of them? Does it also clash if the labelset of a series a subset of another series? if so, then TIL :)

[pracucci]

If all other instances of the results cache have the component label in their metrics, why do the query-frontend results cache metrics clash with any of them? Does it also clash if the labelset of a series a subset of another series? if so, then TIL :)

We register the same metric name multiple times. To make it work, it must have the same exact constant label names but with different values (to not clash). We were already using the component const label for that purpose in all places, except the query-frontend results cache.

[pracucci]

Since this logic is very difficult to enforce with unit tests, I've added an integration test. It breaks with the version currently in main.