Add logging to the Rust vss-server

[tnull]

Aside from some messages written to stdout on startup, we currently don't support any kind of logging. We should add support for proper per-request logging (TRACE, and possibly DEBUG in case of a failure) to allow for a better debugging experience.

While a more advanced approach such as #75 could be nice eventually, we should probably for now just start out with an approach similar to what LDK Server does: use the log facade for the actual logging, but consume it via a simple local logger module to avoid taking on any unnecessary dependencies. Basically, we should be able to just copy over https://github.com/lightningdevkit/ldk-server/blob/main/ldk-server/src/util/logger.rs