Add /converttodm and /converttoroom commands

### Your use case

#### What would you like to do?
Add /convertodm and /converttoroom commands just like on the Element Web.

#### Why would you like to do it?
Sometimes mechanism detecting whenever a room is a DM fails, especially after creating a DM with a person already chatted with before.
As long as the DM detection needs improvements, such commands would make troubleshooting much simplier.
Example scenario: after months of chat with a friend, turned out his Element X client does not treat our room as DM. I needed to instruct him how to login into Element Web and type the command.

### Have you considered any alternatives?

_No response_

### Additional context

_No response_

### Are you willing to provide a PR?

No