sever+lncfg: add sweepr config

[yyforyongyu]

This PR adds the ability to customize sweeper config, which is needed to set up special cases for our itest. This can also be useful to customize the sweeper behavior.

We may also consider making a RPC server for sweeper to have better control over the sweeping process.

[guggero]

Very nice refactor!
Just a few thoughts around the safety aspect of this.

[Crypt-iQ]

Can we make these configurable only with like an itest build flag? I feel like users will footgun themselves if they can configure something like DefaultMaxSweepAttempts. If this particular limit is reached, then the contract resolvers will "give up" until a restart, which can be dangerous if the limit is low

[Roasbeef]

Nice, I've run into some issues w/ this in the past when a sweep actually comes after some target event, and then needs to backoff, which causes a test failure or some non-deterministic behavior.

[yyforyongyu]

Can we make these configurable only with like an itest build flag? I feel like users will footgun themselves if they can configure something like DefaultMaxSweepAttempts. If this particular limit is reached, then the contract resolvers will "give up" until a restart, which can be dangerous if the limit is low

Probably shouldn't put more changes than needed in this PR, so the other config options are now removed. Also does this mean DefaultMaxSweepAttempts of 10 is sometimes not enough?

Still thinking about the RPC server, or at least creating a new method to allow fetching the UtxoSweeper.pendingInputs. This way we could do more explicit checks over the sweeping txes rather than relying on checking the mempool. A future PR tho.

[Roasbeef]

LGTM 🐊

[Roasbeef]

Needs a rebase!

[yyforyongyu]

Needs a rebase!

Done!