It was previously using jobcontrol to achieve this, but that apparently
doesn't work when there is no tty. This makes it so that it directly
handles SIGINT and SIGTERM and passes it on to tailscaled. I tested this
works on a Digital Ocean K8s cluster.
Fixes#5512
Signed-off-by: Maisem Ali <maisem@tailscale.com>
This has the benefit of propagating SIGINT to tailscaled, which in turn
can react to the event and logout in case of an ephemeral node.
Also fix missing run.sh in Dockerfile.
Signed-off-by: Maisem Ali <maisem@tailscale.com>