This PR makes it so the Consul sync logic will ignore operations that
do not specify an action to take (i.e. [de-]register [services|checks]).

Ideally such noops would be discarded at the callsites (i.e. users
of [Create|Update|Remove]Workload], but we can also be defensive
at the commit point.

Also adds 2 trace logging statements which are helpful for diagnosing
sync operations with Consul - when they happen and why.

Fixes #10797