* Revert "PLT-5765 Passed SiteURL to SendNotifications (#5705)"
This reverts commit a8e68bd890.
* Removed automatic configuration of SiteURL
* Reverted unintentional config changes
* Updated help text
* Added link to docs in Site URL warning
* Fixed merge conflict
* Added separate post types for system_join_leave and system_add_remove posts
* Added username prop to channel deleted posts
* Changed slack import to properly generate the new join/leave messages
* Added username prop to channel update posts
* Moved Post(AddTo/RemoveFrom)ChanneMessage into app package
This commit provides the first part of the bulk import system.
The CLI command is provided, complete with validation & apply modes. All
the basic properties of Teams and Channels can be imported. Users &
Posts will follow separately in a future commit.
This fixes the issue where the channel fails to Import from Slack if
there is already a channel with the same name on Mattermost that has
been deleted.
