Add support for user defined annotations on StatefulSet

[AfonsoFGarcia]

The goal of this PR is to enable the StatefulSet to be annotated, for tools like keel to work with this chart.

For example, the following values.yaml:

statefulSetAnnotations:
  keyOne: valueOne
  keyTwo: valueTwo

Would be included in the StatefulSet as:

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: home-assistant
  annotations:
    keyOne: valueOne
    keyTwo: valueTwo

Sorry for the 3 commits, was doing this from the web UI. If you prefer, I can squash them.

[pajikos]

Thank you