refactor: simplify leader election

[acuteaura]

mostly based on the upstream example:
https://github.com/kubernetes/client-go/blob/master/examples/leader-election/main.go

this also incidentally fixes bugs where run returns nil (i.e. when failing to reach the Admin API) by causing the context to cancel via defer.

• Bugfix
• Refactor

[acuteaura]

some remarks on this PR:

• a bunch of code seems to treat leader status as "skipping writes" (via the Elector). this is pretty hard to reason about and prone to errors, so this PR changes it to a more traditional standby (with informers warmed up) that doesn't run any controllers.
• alongside that, the controller now hard exits when it loses leader status. this likely only happens when a node netsplits from k8s apiserver, so it wouldn't be able to update things there anyway.
• run got an error return value, because a lot of error conditions were just silently discarded. A future PR should improve these errors with some kind of wrapping and remove explicit logging in run itself so it all bubbles up
• I did not touch the API server, because I'm not 100% about all the things it does, but we should consider failing a readiness probe if it is not leader if code in there relies on controllers running - though it did not have access to Elector until this point either.

[Revolyssup]

@acuteaura Can you fix the merge conflicts?

[Revolyssup]

@acuteaura Unit tests failing

[Revolyssup]

Makes sense

[Revolyssup]

an e2e test related to leader election was also failing. I reran it

[acuteaura]

The unit test is testing specific strings in the output instead of functionality, I think it can go.

The e2e test.... I don't even know, it seems to fail before setup, but the Restart Count between the describe and the get are different and... it doesn't make sense to me why this test would fail its BeforeRun.

[acuteaura]

@Revolyssup could you have a look at this failed test? I'm not really sure how it could fail in the beforeEach step when that's all shared among tests. Or maybe re-run the tests to make sure this isn't a flake.

It's unfortunately not so trivial to run this test locally, but I'm getting to it...

[zll600]

ping @Revolyssup

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