fix(interaction_metadata): document command_type

[ImRodry]

This PR documents the command_type key that is sent on the interaction_metadata object of a Message. Not sure why this wasn't documented as the PR that added the object (#6723) did not have any discussion on it. I purposely left out the name property as a previous PR adding this was rejected (#6734) but I don't see anything against this property. It would be helpful to document both in order to be able to fully stop using interaction in favor of interaction_metadata

[ImRodry]

Removed name, reopening to get feedback on command_type

[Soheab]

Bump. Would be nice if name was documented too...