Start watching mempool in htlc outgoing contest resolver

[yyforyongyu]

This is a follow-up PR from #7564, where we start watching preimage in mempool in our HTLC outgoing contest resolver too to have a faster preimage extraction. Depends on,

• #7811

[saubyk]

Concept Ack

[ProofOfKeags]

Seems like this one is languishing, how can I move it along, and is it priority enough to focus on? I keep ignoring the notifs on it because my review hasn't been re-requested but I wanted to figure out if ignoring it is the wrong thing.

[yyforyongyu]

@ProofOfKeags thanks for asking! I think this PR just needs one more approval then it can be merged. It's not urgent imo but nice to have - maybe it will become more urgent once the sweeper is done, as we've made some assumptions about the mempool there.

[lightninglabs-deploy]

@crypt-iq: review reminder @roasbeef: review reminder @yyforyongyu, remember to re-request review from reviewers when ready

[yyforyongyu]

!lightninglabs-deploy mute 720h30m

[yyforyongyu]

!lightninglabs-deploy mute 720h30m

[lightninglabs-deploy]

@crypt-iq: review reminder @roasbeef: review reminder @yyforyongyu, remember to re-request review from reviewers when ready

[yyforyongyu]

!lightninglabs-deploy mute