In some configurations, user explicitly do not want to store
tailscale state in k8s secrets, because doing that leads to
some annoying permission issues with sidecar containers.
With this change, TS_KUBE_SECRET="" and TS_STATE_DIR=/foo
will force storage to file when running in kubernetes.
Fixes#6704.
Signed-off-by: David Anderson <danderson@tailscale.com>
We still have to shell out to `tailscale up` because the container image's
API includes "arbitrary flags to tailscale up", unfortunately. But this
should still speed up startup a little, and also enables k8s-bound containers
to update their device information as new netmap updates come in.
Fixes#6657
Signed-off-by: David Anderson <danderson@tailscale.com>
