Optionally support $toObjectId in MongoDB adapter

[0x557269656C]

Hi Community 👋🏻

After upgrading to the latest version of the library, I've appreciated the decoupling of mongoose models, however in my setup I needed to support ObjectId and had to virtual (monkey) patch my MongoDB adapter's getSessionAndUser().

This sort of patching is not ideal and I recognise there may be hesitance to introduce further customisation options to the MongoDB adapter, but given that this particular change could be driven by an optional pipeline stage such as:

{ $addFields: { user_id: { $toObjectId: "$user_id" } } }

Would it be proper to include an option like {coerceObjectId: true} (or a suitable naming alternative) to facilitate this?
Perhaps the option to provide a custom pipeline?

Looking forward for your takes on this, thank you all for your time!