Add alternative "I trust my counterparty (who is an LSP)" UserConfig defaults

[TheBlueMatt]

We have a lot of users who use LDK with a counterparty who is their LSP and they trust to not play games with dust limit/feerates and maybe even accept 0conf channels from. We should have an alternative UserConfig defaults constructor for these users which avoids a lot of pitfalls and accidental force-closures.

[valentinewallace]

Potentially relevant for async payments (cc #2298) as well, as LDK will need to know whether it is an often-offline sender/recipient when paying and generating offers respectively, as well as which of its counterparties are LSPs.

[TheBlueMatt]

Would be cool if this somehow disabled the min-feerate checks entirely.