[tests] tailscale integration test

[kylos101]

Is your feature request related to a problem? Please describe

We lack integration tests that tell us about the health of our support for the tailscale feature.

Describe the behaviour you'd like

Our integration tests should assert that the tailscale integration, including support for DNS, is working as expected.

Describe alternatives you've considered

Continue doing manual testing.

Additional context

gitpod-io/workspace-images#956
https://github.com/gitpod-io/website/pull/2908
#13785

Adding secrets to support this test.

1. Add the secret to GCP (manually) in gitpod-core-dev project
2. Copy the secret from GCP to core-dev with TF (docs)
3. Copy the secret from core-dev to the preview environment as part of the deploy (example)

The secret you'll be storing is a tailscale key (authkey). It should be reusable (so it can support many preview VMs) and ephemeral (so when machines go offline from the tailscale network, that they are removed).

[kylos101]

Updated ☝ to account for secrets management