Plugin API hook for Shared Channel file attachment sync (#25874)

* option for auto inviting plugin to all shared channels.

* auto-invite remotes to shared channels when flag set

* fix unit test

* immediately ping new remotes; fix unique siteurl bug

* make i18n-extract

* fix translations

* plugin hooks for file attachments

* hook for profile image sync

* fix profile image sync

* fix unit test

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Co-authored-by: Mattermost Build <build@mattermost.com>

server/platform/services/sharedchannel/service.go

@@ -64,6 +64,8 @@ type AppIface interface {
 	InvalidateCacheForUser(userID string)
 	NotifySharedChannelUserUpdate(user *model.User)
 	OnSharedChannelsSyncMsg(msg *model.SyncMsg, rc *model.RemoteCluster) (model.SyncResponse, error)
+	OnSharedChannelsAttachmentSyncMsg(fi *model.FileInfo, post *model.Post, rc *model.RemoteCluster) error
+	OnSharedChannelsProfileImageSyncMsg(user *model.User, rc *model.RemoteCluster) error
 }
 
 // errNotFound allows checking against Store.ErrNotFound errors without making Store a dependency.