subserver: add tarod sub-server as both integrated and remote operating mode

[Roasbeef]

Is your feature request related to a problem? Please describe.

Today user can't use litd to interact with tarod. Adding this tarod to litd would streamline the deployment of things like Taro-aware Loop In/Out and also auction related features in Pool.

Describe the solution you'd like

Add tarod as a sub-server. Ideally via both the integrated and the remote operating mode. tarod was designed to be easily slotted in as an integrated sub-daemon, as it was baed on some of the refactorings we did on the pool/loop side to make that possible.

Additional context

Along the way to doing this, we might want to pick up this PR again: #442

This would allow us to better carve out the framework needed to add/maintain sub-servers in the daemon.

Along the way, we'd also want to make sure that the existing LNC stack works seamlessly.

[ellemouton]

fixed in #550