Containers are typically immutable and should be updated as a whole (and
not individual packages within). Deny enablement of auto-updates in
containers.
Also, add the missing check in EditPrefs in LocalAPI, to catch cases
like tailnet default auto-updates getting enabled for nodes that don't
support it.
Updates #11544
Signed-off-by: Andrew Lytvynov <awly@tailscale.com>