The operator creates a non-reusable auth key for each of
the cluster proxies that it creates and puts in the tailscaled
configfile mounted to the proxies.
The proxies are always tagged, and their state is persisted
in a Kubernetes Secret, so their node keys are expected to never
be regenerated, so that they don't need to re-auth.
Some tailnet configurations however have seen issues where the auth
keys being left in the tailscaled configfile cause the proxies
to end up in unauthorized state after a restart at a later point
in time.
Currently, we have not found a way to reproduce this issue,
however this commit removes the auth key from the config once
the proxy can be assumed to have logged in.
If an existing, logged-in proxy is upgraded to this version,
its redundant auth key will be removed from the conffile.
If an existing, logged-in proxy is downgraded from this version
to a previous version, it will work as before without re-issuing key
as the previous code did not enforce that a key must be present.
Updates tailscale/tailscale#13451
Signed-off-by: Irbe Krumina <irbe@tailscale.com>