Automatic merge from submit-queue
Respect PDBs during node upgrades and add test coverage to the ServiceTest upgrade test.
This is still a WIP... needs to be squashed at least, and I don't think it's currently passing until I increase the scale of the RC, but please have a look at the general outline. Thanks!
Fixes#38336
@kow3ns @bdbauer @krousey @erictune @maisem @davidopp
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On GCE, node upgrades will now respect PodDisruptionBudgets, if present.
```