Add serviceAccount annotations

[blakelead]

ServiceAccount annotations

Why

Public Cloud Providers use serviceAccount annotations to enable pod identity.

What

Annotations for serviceAccount can be set like this:

serviceAccount:
  create: true
  name: instana-agent
  annotations:
    iam.gke.io/gcp-service-account: instana@xyz.iam.gserviceaccount.com

Checklist

• Backwards compatible?
• Documentation added to the README.md?
• Changelog updated?

[Milica-Cvrkota-IBM]

We will incorporate changes in our internal repository, thanks! This repo just hosts the source of the charts so we can't merge the changes here

[blakelead]

Thanks for integrating this change