fix(kuma-cp): don't unset disconnectTime in ZoneInsight subscriptions

[michaelbeaumont]

I think ZoneInsightSink can unset disconnectTime that has been marked disconnected in UpdateSubscription because it doesn't take the value from the current ZoneInsight but rather takes the subscription instead from streamState.

Changing this in UpdateSubscription is one way to ensure this doesn't happen.

See #7535

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) --
  • 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) --

[jakubdyszkiewicz]

I'm not sure this is a right approach to be honest.
subscription in stream state means that it was not disconnected, right?

[michaelbeaumont]

I'm not sure this is a right approach to be honest.
subscription in stream state means that it was not disconnected, right?

Does it? I'll admit I don't fully understand everywhere that's writing to ZoneInsight but this only triggers if the disconnectTime was previously set. If a subscription in stream state means it isn't disconnected, how can we tolerate having disconnectTime automatically set in UpdateDescription?

[michaelbeaumont]

#8153