[FLINK-36353][Flink Operator Helm chart] Allow to add affinity for operator pod of helm chart

[gaddam1987]

What is the purpose of the change

The change allows the flink operator pod to be assigned a node based on pod affinity which gives more flexibility

Brief change log

• Allow pod created by flink operator to define affinity, so it is more flexible to select a node where the pod can start

Verifying this change

This change is a trivial rework / code cleanup without any test coverage.

• Just a change in K8 env to add a affinity. Node slector is already supported but in some cases its nice to have (https://kubernetes.io/docs/concepts/scheduling-eviction/assign-pod-node/#affinity-and-anti-affinity)

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (yes / no) No
• The public API, i.e., is any changes to the CustomResourceDescriptors: (yes / no) No
• Core observer or reconciler logic that is regularly executed: (yes / no) No

Documentation

• Does this pull request introduce a new feature? (yes / no) No
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)