Automatic merge from submit-queue (batch tested with PRs 43871, 44053)
Proxy healthchecks overhaul
The first commit is #44051
These three commits are tightly coupled, but should be reviewed one-by-one. The first adds tests for healthchecks, and found a bug. The second basically rewrites the healthcheck pkg to be much simpler and less flexible (since we weren't using the flexibility). The third tweaks how healthchecks are handled in endpoints-path to be more like they are in services-path.
@MrHohn because I know you were in here for source-IP GA work.
@wojtek-t
033bf6fd8b