fix(kuma-cp): cancel OnTick when watchdog stopped

[michaelbeaumont]

If SimpleWatchdog.OnTick from the dataplaneWatchdogFactory, i.e. snapshot generation, takes a very long time and the proxy disconnects and reconnects, the Context used in OnTick is never canceled, because OnTick never returns and we thus never see stop being closed.

Additionally, we did not pass an OnTick Context down into the Generators, in particular, to generateCerts.

• fix(kuma-cp): pass context via snapshot reconciler to generateCerts #7231

I intentionally don't touch hds, mads or kds with this PR.

• noticed while testing locally but CP recovers: OnTick error: metadata cannot be nil?
  • We're calling Cleanup now, which removes the metadata from the node, which causes this error. But we recover when the metadata tracker adds the metadata. Is this acceptable (for now)?
  • @slonka @bartsmykla WDYT? this is a good example of an "error" that's not an alarming error
  • fix(kuma-cp): put metadata xds callbacks before sync #7230

Checklist prior to review

• 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?

[slonka]

WDYT? this is a good example of an "error" that's not an alarming error

might be interesting to know why it's nil, but if it recovers in 100% cases than switch from error -> warn

[github-actions]

backporting to release-2.0 with action

backporting to release-2.1 with action
backporting to release-2.2 with action
backporting to release-1.8 with action