Datastore Index Terraform

[brunobowden]

Summary

I'm not clear on what index is being used for Datastore but that should be automatically updated too: https://www.terraform.io/docs/providers/google/r/datastore_index.html

Checklist:

• [x] Searched the existing issues to ensure you are not creating a duplicate.
• [x] Followed the Contributor Guidelines.

[brunobowden]

No index needed for now, so punt until it is needed