mongo: move MongoInfo type

This PR moves the `MongoInfo` type from the `environmentserver/authentication` package to the `mongo` package.

This change is necessary to unblock a larger change which was hitting a circular dependency.

With that said, as this change consists of _removing_ the import of the `environmentserver/authentication` from most packages (and renaming the type), it seems clear in hindsight that the `MongoInfo` type belongs in the `mongo` package.
I'm wondering if you'd consider renaming the struct from MongoInfo to ConnectionInfo, so the other sites that use it will have `mongo.ConnectionInfo`.  Thoughts?