feat(kuma-cp): add observability to k8s auth cache

[jakubdyszkiewicz]

Checklist prior to review

This PR adds missing observability to k8s auth cache.
Additionally we may want to switch to go burrow for other caches (to have bounded cache), however I don't want to do it in this PR.
Prometheus stats counter is in utils, because it will be reused in Kong Mesh.

• Link to relevant issue as well as docs and UI issues --
• This will not break child repos: it doesn't hardcode values (.e.g "kumahq" as a image registry) and it will work on Windows, system specific functions like syscall.Mkfifo have equivalent implementation on the other OS --
• Tests (Unit test, E2E tests, manual test on universal and k8s) --
• Do you need to update UPGRADE.md? --
• Does it need to be backported according to the backporting policy? --
• Do you need to explicitly set a > Changelog: entry here or add a ci/ label to run fewer/more tests?

[michaelbeaumont]

LGTM