During the integration tests we might want to shut down a trader client
through the admin RPC. If that closes the shutdown channel on a package
global interceptor, that means we can't start another trader client
during that test. We need to make sure we can pass in an interceptor for
each trader instance.
With this commit we add a new sidecar acceptor type that is exclusively
responsible for managing the recipient's tasks of executing a sidecar
channel. The two tasks are:
1. Verify a sidecar ticket and the offer contained within then add the
recipient node information to the ticket so it can be returned to the
sidecar provider. This is step 2/4 of the entire sidecar execution
protocol.
2. Interact with the auction server and connect out to an asker's node in the
right moment then accept the incoming channel. This is step 4/4 of the
entire sidecar execution protocol.
The code for these two tasks are kept separate from the default funding
manager to make it easier to extract a standalone sidecar acceptor
client later on. It also makes it easier to see what code would need to be
re-implemented in another language to integrate just the acceptor part.
