Our existing container-detection tricks did not work on Kubernetes,
where Docker is no longer used as a container runtime. Extends the
existing go build tags for containers to the other container packages
and uses that to reliably detect builds that were created by Tailscale
for use in a container. Unfortunately this doesn't necessarily improve
detection for users' custom builds, but that's a separate issue.
Updates #13825
Signed-off-by: Tom Proctor <tomhjp@users.noreply.github.com>
