* Slack: Add support for (some) groups
Some of the older private channels in the workspace I'm working in have channel ID's starting with `G0` and `GF` and this resulted to false positive `channel_not_found` errors.
I've added these prefixes to the list to maintain as much backwards compatibility as possible.
Ideally the auto-prefix of the channel name with `#` is dropped entirely, given the Channel ID's have become more dominant in the Slack API over the past years.
* Add changelog fragment for slack channel prefix fix
* Update changelogs/fragments/5019-slack-support-more-groups.yml
Co-authored-by: Felix Fontein <felix@fontein.de>
Co-authored-by: Felix Fontein <felix@fontein.de>
