I went back and dug through all of the "what functions can throw what
types", and made sane decisions about them. boost errors are
aggressively translated into FDB ones, whcih might result in multiple
lines of logging about errors, but this is in infrequently run code, so
it should be fine.
The idea being that we keep around a TLSConfig that the configuration
that the user has provided, and then when we want to intialize an SSL
context, we ask the TLSConfig to load all certificates and return us a
LoadedTLSConfig that is a concrete set of certificate bytes in memory.
initTLS now just takes the in-memory bytes and applies them to the ssl
context.
This is a large refactor to lead up into certificate refeshing, where we
will periodically check for changes to the certificates, and then
re-load them and apply them to a new SSL context.
