Cannot create new channel from IRC

[setpill]

When /joining a non-existent channel, a new Mattermost channel should be created and joined.

[42wim]

For those that want to make a PR for this, make sure to make this feature an option in matterircd.toml which is false by default.

[hloeung]

I feel like this is likely to create a bunch of typo channels - ones no one will likely use the UI to go and delete/purge. I agree with Wim on making sure it defaults to disabled.

So the change would basically be, on join getChannelIdTeam(), if no channel ID found or returned from , call CreateChannel() or similar.

[kot0dama]

Maybe this could be achieved through a /msg mattermost create-channel #whatever instead of a simple /join ?
That would not reduce the risk of typos but would ensure the goal is to indeed create a new channel.

[hloeung]

I think this is a good path forward and related to the issue/wishlist you raised in #568