fix(sidecar): ping messages were not sent

[thedevbirb]

This PR fixes the ping of the CommitmentRequestProcessor. In essence, pings were sent only if other events woke up the task because the receiver is not using the asynchronous context.
Moreover, a broadcast receiver doesn't track individual tasks or their wakers. As such, I've opted to completely remove the PingTicker and use an interval instead spawned per task, that once ticked sends ping messages.

[merklefruit]

Have you considered moving from sync::broadcast to sync::watch channels?
Perhaps useless for the ping one since it needs to send repeated messages but can be useful to fix the shutdown one.

[thedevbirb]

Have you considered moving from sync::broadcast to sync::watch channels? Perhaps useless for the ping one since it needs to send repeated messages but can be useful to fix the shutdown one.

Added a workaround with 987410d. #673 would be a generalized solution.

[merklefruit]

LGTM

[mempirate]

Good stuff, the peculiarities of async rust init