resource manager implementation

[elnosh]

Part of #4384

This PR introduces a ResourceManager trait and DefaultResourceManager implementation of that trait which is based on the proposed mitigation in lightning/bolts#1280.

It only covers the standalone implementation of the mitigation. I have done some testing with integrating it into the ChannelManager but that can be done separately. As mentioned in the issue, the resource manager trait defines these 4 methods to be called from the channel manager:

• add_channel
• remove_channel
• add_htlc
• resolve_htlc

Integrating into the ChannelManager

• The ResourceManager is intended to be internal to the ChannelManager rather than users instantiating their own and passing it to a ChannelManager constructor.

• add/remove_channel should be called when channels are opened/closed.

• add_htlc: When processing HTLCs, the channel manager would call add_htlc which returns a ForwardingOutcome telling it whether to forward or fail the HTLC along with the accountable signal to use in case that it should be forwarded. For the initial "read-only" mode, the channel manager would log the results but not actually fail the HTLC if it was told to do so. A bit more specific on where it would be called: I think it will be when processing the forward_htlcs before we queue the add_htlc to the outgoing channel

  rust-lightning/lightning/src/ln/channelmanager.rs

  Line 7650 in caf0aac

  if let Err((reason, msg)) = optimal_channel.queue_add_htlc(

• resolve_htlc: Used to tell back the ResourceManager the resolution of an HTLC. It will be used to release bucket resources and update reputation/revenue values internally.

This could have more tests but opening early to get thoughts on design if possible

cc @carlaKC