Support health probes for sidecar containers in cluster manifest

Please, answer some short questions which should help us to understand your problem / question better?

• Which image of the operator are you using? registry.opensource.zalan.do/acid/postgres-operator:v1.5.0
• Where do you run it - cloud or metal? Kubernetes or OpenShift? Bare Metal K8s
• Are you running Postgres Operator in production? yes
• Type of issue? Feature request

For certain types of sidecar containers, it would be nice to be able to define health probes (liveness, readiness, startup).
Unfortunately, the Sidecar struct in the cluster manifest doesn't allow probe definitions, which could be easily added (or could the Sidecar struct be replaced entirely in favor of a full v1.Container spec?)

Would this be an interesting feature addition, or am I missing a general problem as to why sidecars are limited to a certain subset of the v1.Container attributes?

I don't have any first-hand experience in operator development but can prepare an initial PR if you are interested!

Locate the Sidecar struct and the cluster-manifest handling that currently limits sidecar attributes. First compare the existing sidecar representation with Kubernetes container probe definitions, then identify the relevant test coverage. Done means liveness, readiness, and startup probes can be defined for sidecars and the behavior is covered by tests.