Clarify docs surrounding raw MongoDB queries

[andrew-walford-prisma]

From Slack thread: https://prisma-company.slack.com/archives/C5Z9TH6N9/p1657703351889459

People want to use raw MongoDB queries but don’t know how to use $runCommandRaw for this. The docs can probably be improved quite a bit (ideally with more examples). Example of user asking about this: https://prisma.slack.com/archives/C0281DB57HQ/p1656395218035119

One user (PinkiePie) wants to know

• what input $runCommandRaw accepts.
• Feels that the example in our docs uses a "useless number" instead of an ObjectID.
• How to tell Prisma that _id is an ObjectID
• Can you pass a string - db.runCommand should accept a string. It doesn't appear that $runCommandRaw can accept a string, but maybe it can - if so, how?

Related issues (we might want to work on these together):

• https://github.com/prisma/docs/issues/3220
• https://github.com/prisma/docs/issues/3209