In this commit, we add a check inside EstimateFeePerKW for bitcoind so
that when the conf target exceeds the maxBlockTarget, we will use
maxBlockTarget instead.
This enforces the _actualized_ fee rate of the commitment transaction,
rather than the fee floor used for estimation. The new value of 250
sat/kw corresponds to 1 sat/byte, rather than 253 which is only rounded
up during estimation to account for the fact that BOLT 3 rounds down to
the nearest satoshi and that the vbyte fee estimation is lossy.
Previously we would incorrectly fail to sign the next commitment even
though the fee was technically high enough. Restarting with this commit
should solve the issue as long as the channel hasn't already gone to
chain.
In this commit, we create a new chainfee package, that houses all fee
related functionality used within the codebase. The creation of this new
package furthers our long-term goal of extracting functionality from the
bloated `lnwallet` package into new distinct packages. Additionally,
this new packages resolves a class of import cycle that could arise if a
new package that was imported by something in `lnwallet` wanted to use
the existing fee related functions in the prior `lnwallet` package.
