optionally disable converting "!"-prefixed commands to "/"-prefixed commands

[maltee1]

When sending a "!"-prefixed matrix command, it gets converted to a "/"-prefixed telegram command. This may be handy at times, but it can also be confusing.

I have a group that's bridged between matrix, signal and telegram. There is a matrix bot in the room that anyone can interact with. It's confusing for telegram users that matrix users can seemingly use the forward slash prefix while they have to use the exclamation mark prefix.

This PR allows disabling that conversion and bridges commands unchanged, thus avoiding confusion.

I suppose an alternative would be to instead convert /telegram commands into !matrix commands so that what telegram users see is consistent.

Not sure if this is something you'd like, just let me know.