Expand lifecycle and probes to sidecars

[retpolanne]

If applied, this PR expands the liveness, readiness and lifecycle to sidecars, such as the NGINX sidecar or the CloudSQL Proxy sidecar.

However, it can be harmful for deployments using CloudSQL Proxy, as the liveness/readiness probe might not work for it.

[codecov-io]

Codecov Report

Merging #618 into master will increase coverage by <.01%. The diff coverage is 88.23%.

@@            Coverage Diff             @@
##           master     #618      +/-   ##
==========================================
+ Coverage   50.16%   50.16%   +<.01%     
==========================================
  Files          86       86              
  Lines        6180     6181       +1     
==========================================
+ Hits         3100     3101       +1     
  Misses       2876     2876              
  Partials      204      204

Impacted Files	Coverage Δ
pkg/server/k8s/converters.go	89.31% <88.23%> (+0.02%)	:arrow_up:

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 4d571ce...d3a8f3a. Read the comment docs.