beckerinj has created PR #1356: Add Database raw_run_command in mongo-rust-driver

Issue Text:
The database `run_command` api only takes a Document, while internally it is later converted to a RawDocumentBuf before execution. In a situation where you already have the command as a RawDocumentBuf in the first place, an unneeded conversion RawDocumentBuf -> Document -> RawDocumentBuf is required to use this API.

I noticed that there was this `RunCommand::new_raw` method, which was feature gated behind "in-use-encryption". I'm not sure the reason for this gate, but it's trivial to remove it and use it with the additional `database.raw_run_command` method added here.

I only added `raw_run_command`, but a similar `raw_run_cursor_command` could also be added which takes RawDocumentBuf as well.