Missing support for affinity in m3db-operator helm chart

[mdfaizsiddiqui]

Thanks for opening an issue for the M3DB Operator! We'd love to help you, but we need the following information included
with any issue:

• What version of the operator are you running? Please include the docker tag. If using master, please include the git
  SHA logged when the operator first starts.
  NA

• What version of Kubernetes are you running? Please include the output of kubectl version.
  NA

• What are you trying to do?

  • Want to add affinity rules for m3db-operator stateful-sets via the helm chart

• What did you expect to happen?

• What happened?