In TS2021 the MachineKey can be obtained from noiseConn.Peer() - contrary to what I thought before,
where I assumed MachineKey was dropped in TS2021.
By having a ts2021App and hanging from there the TS2021 handlers, we can fetch again the MachineKey.
0.16.0 introduced random suffixes to all machine given names
(DNS hostnames) regardless of collisions within a namespace.
This commit brings Headscale more inline with Tailscale by only
adding a suffix if the hostname will collide within the namespace.
The suffix generation differs from Tailscale.
See https://tailscale.com/kb/1098/machine-names/
OIDC might be configured, but unable to be initialised, this only runs
the oidc cycle if it is actually successfully set up/initialised.
Prep for next commit
Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>
