* tonic-health: commit generated code rather than generating at build time
This saves users from needing protoc available on their path if they're not
generating other tonic code at build time, either.
The generated modules can be regenerated by enabling the `gen-proto`
feature, which will trigger the relevant part of the build script.
* Check generated code for tonic-health matches in CI
* Use bootstrap test to generate/check validity of generated code
As suggested by @LucioFranco in https://github.com/hyperium/tonic/pull/1065\#discussion_r951580189.
This avoids the need for a feature which would show
up in docs.rs, and achieves the same goals via CI.
