CXX-360 add support for authMechanismProperties

Our SASL implementation seems to only have support for SERVICE_NAME, so I left the others out. They are listed as "MAY IMPLEMENT" in the spec anyway.


If this is a novel initializer, you need to use the init functions magic to make sure it gets linked. @hanumantmk can show you how to do it or you can figure it out by looking at some other files with mongo inits in them.