api/maintenance: add alarm/health information in endpoint status

[gyuho]

#9162 removes "errors" field from /health endpoint.

Better place to serve this information is etcdserverpb.StatusResponse. Probably, just add another repeated field of errors.

[gyuho]

@dvonthenen Do you want to work on this (very similar to #9176)?

[davidvonthenen]

@gyuho Sure thing! If you have any other ones, just let me know.

[davidvonthenen]

@gyuho Do we want to also expose these errors on the etcdctl table output?

[gyuho]

@dvonthenen Yes. Thanks!

[davidvonthenen]

No problem

[davidvonthenen]

PR #9206 submitted

[davidvonthenen]

I believe this issue can be closed since PR #9206 has been merged. Thanks!

[xiang90]

@dvonthenen thanks for the contribution.