Mattermost 6.6: Important upgrade notes

@twk3 Below is a note of important upgrade notes in our upcoming release.

Mattermost v6.6 (GitLab 14.11 - May 22)

  • The Apps Framework protocol for binding/form submissions has changed, by separating the single call into separate submit, form, refresh and lookup calls. If any users have created their own Apps, they have to be updated to the new system.
Edited by Amy Blais