Currently, it seems that the default set of Codecs supports just `Map<String, Object>`. This is fine for many use cases, but there is often the use case to use any number of key types.

Currently, I have a (most likely/ obviously) sub-optimal solution that looks like this: https://stackoverflow.com/questions/67849754/mongodb-mapk-v-codec-maps-must-have-string-keys-fix (not my code)

This works most of the time, but seems to hate `Map<ObjectId, *>` types.

There should be a standardized codec that can handle any type of map.