Secretstore: GCP Secrets Manager to support implicit credentials

[tholcman]

Support implicit credentials (f.e. Workload Identity in k8s) for GCP Secrets Manager client creation like it does for pubsub client:

this function
https://github.com/dapr/components-contrib/blob/master/secretstores/gcp/secretmanager/secretmanager.go#L66

should be similar to this one
https://github.com/dapr/components-contrib/blob/master/pubsub/gcp/pubsub/pubsub.go#L152

[dapr-bot]

This issue has been automatically marked as stale because it has not had activity in the last 30 days. It will be closed in the next 7 days unless it is tagged (pinned, good first issue, help wanted or triaged/resolved) or other activity occurs. Thank you for your contributions.

[dapr-bot]

This issue has been automatically closed because it has not had activity in the last 37 days. If this issue is still valid, please ping a maintainer and ask them to label it as pinned, good first issue, help wanted or triaged/resolved. Thank you for your contributions.

[tholcman]

Please don't close this feature request, I guess it is important for security and also for consistency - pubsub component supports, it should be supported also by secrets component!