feat(kds): stats of kds client versions

[jakubdyszkiewicz]

Checklist prior to review

This PR adds stats of number of clients per version. For now it only works with Delta KDS, but I added this to generic stats callbacks so in the future we can add this to other DSes if we want to.

I considered just adding a dimension to _streams_active metric, but streams active counts all DS streams, whereas this metric only counts streams with at least one DiscoveryRequest, because version is carried in metadata of request. This should be equal, but technically can be different.

• 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) --
  • Don't forget ci/ labels to run additional/fewer tests
• Do you need to update UPGRADE.md? --
• Does it need to be backported according to the backporting policy? (this GH action will add "backport" label based on these file globs, if you want to prevent it from adding the "backport" label use no-backport-autolabel label) --