Prep for MS Teams plugin API (#25565)

* - columns added to ShareChannelRemotes: lastpostcreateat, lastpostupdateat
- SyncMsg and SyncResponse moved to `model` package
- field added to RemoteCluster struct: PluginID

* sync new posts before updated posts to ensure post order in MS Teams

* add plugid to remoteclusters table and store

* don't sync history by default

server/public/model/post.go

@@ -327,13 +327,20 @@ type GetPostsSinceOptions struct {
 
 type GetPostsSinceForSyncCursor struct {
 	LastPostUpdateAt int64
-	LastPostId       string
+	LastPostUpdateID string
+	LastPostCreateAt int64
+	LastPostCreateID string
+}
+
+func (c GetPostsSinceForSyncCursor) IsEmpty() bool {
+	return c.LastPostCreateAt == 0 && c.LastPostCreateID == "" && c.LastPostUpdateAt == 0 && c.LastPostUpdateID == ""
 }
 
 type GetPostsSinceForSyncOptions struct {
 	ChannelId       string
 	ExcludeRemoteId string
 	IncludeDeleted  bool
+	SinceCreateAt   bool // determines whether the cursor will be based on CreateAt or UpdateAt
 }
 
 type GetPostsOptions struct {