Background probing service #765
Description
We should allow LDK Node (and then eventually Server) to run in a background probing service mode, i.e., have a background task running that periodically probes paths with certain characteristics. To that end, users should be able to configure:
- Probing strategy (probably choosing from some pre-defined strategies, possibly also a custom strategy)
- How much of the local liquidity should be used for probing at max
- How often probes should be sent / how often old data should be refreshed
Relevant discussion: #678 was a first shot at this but didn't get very far.