Support impersoante service account

[yu-iskw]

TL;DR

I would like to get Google Cloud Secret Manager secrets with an impersonate service account.

Detailed design

    - id: 'secrets'
      uses: 'google-github-actions/get-secretmanager-secrets@v1'
      with:
        impersonate_service_account: "test@test-project.iam.gserviceaccount.com"
        secrets: |-
          token:my-project/docker-registry-token

Additional information

No response