Echo SSH output to the GitHub Action logs

[teor2345]

TL;DR

Add a show_ssh_output input to the action, which shows the SSH stdout and stderr in the GitHub Action logs. Ideally, the output should be shown live, as it arrives over SSH.

Detailed design

This feature allows the ssh-compute action to replace a manual call to gcloud compute ssh, which echoes the SSH output as it arrives, and has no output size limits.

Example usage:

jobs:
  job_id:
    permissions:
      contents: 'read'
      id-token: 'write'

    steps:
    - uses: 'actions/checkout@v2'

    - id: 'auth'
      uses: 'google-github-actions/auth@v0'
      with:
        workload_identity_provider: 'projects/123456789/locations/global/workloadIdentityPools/my-pool/providers/my-provider'
        service_account: 'my-service-account@my-project.iam.gserviceaccount.com'

    - id: 'compute-ssh'
      uses: 'google-github-actions/ssh-compute@v0'
      with:
        instance_name: 'example-instance'
        zone: 'us-central1-a'
        ssh_private_key: '${{ secrets.GCP_SSH_PRIVATE_KEY }}'
        command: 'echo Hello world'
        show_ssh_output: true

Expected behaviour:

Hello world is echoed live by the compute-ssh step, without the need for an extra step.

Additional information

GitHub Actions outputs are limited to 1 MB, so they can't be used for large logs:
https://docs.github.com/en/actions/creating-actions/metadata-syntax-for-github-actions#outputs-for-docker-container-and-javascript-actions

One alternative is using artifacts, but they aren't available live, only after the job has finished:
https://docs.github.com/en/actions/using-workflows/storing-workflow-data-as-artifacts