Upgrade db (in production and dev) to v6

[vnugent]

Mongo version 6 is available on our hosting provider and I'd like to upgrade at some point to improve edit history tracking - being able to record both "before" and "after" when recording a change. Right now we only capture the after. To get the before version we will need to do a nontrivial query.

https://www.mongodb.com/blog/post/change-streams-mongodb-6-0-support-pre-post-image-retrieval-ddl-operations

[zichongkao]

Very supportive for #296 (comment)