Integrate in CI and align with the golangci-lint rules

[dmvolod]

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

• Which image of the operator are you using? e.g. registry.opensource.zalan.do/acid/postgres-operator:v1.7.1
• Where do you run it - cloud or metal? Kubernetes or OpenShift? [Bare Metal K8s]
• Are you running Postgres Operator in production? [no]
• Type of issue? [feature request]

It would be nice to have support golangci-lint in CI and golang code with the base rules.
This makes code more clear, secure and compliant.