* Denormalize Reactions to add ChannelId for top reactions insights query
* Remove hardcoded timestamps
* Fix store, api4 tests for reactions
* Fix tests
* Fix integrity tests, allow reaction to have ChannelId populated before calling store function
* Lint fixes
* Add ChannelId field to BulkGetForPosts, Delete store handlers
* Add index to mysql migration, add not null characteristic without a separate command
* Select channelId instead of fetching post via store.GetPost, add if exists to drop column
* Make updating of Reactions conditional to support pre-migration
Co-authored-by: Mattermod <mattermod@users.noreply.github.com>