feat(kuma-cp): better xds metrics

[jakubdyszkiewicz]

Checklist prior to review

This PR adds labels to xds_generation metric.

result label:

• skip - whenever we decide that we don't need to generate config (mesh hash did not change)
• generated - whenever we generated config, but it was the same
• changed - whenever we generated config and the config was actually different

I also added label of proxy type, because we don't have mesh hash protection for zone ingress and egress so it would be impossible to track how many times XDS was really generated.

This is useful because

• We can track if the environment is stable, a counter of generated or changed is not incremented.
• We can check generated metrics to see if we can maybe do a better job on detecting if we need to even generate XDS config.

This change is backwards compatible with current dashboards with one small exception - previously we were observing the metrics on .Sync error, but we should not do this. We have a separate metric for tracking errors, so I fixed this.

• 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?