MM-33544 is_following prop in getPosts API methods (#17093)

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

model/post.go

@@ -101,6 +101,7 @@ type Post struct {
 	ReplyCount   int64         `json:"reply_count" db:"-"`
 	LastReplyAt  int64         `json:"last_reply_at" db:"-"`
 	Participants []*User       `json:"participants" db:"-"`
+	IsFollowing  bool          `json:"is_following" db:"-"` // for root posts in collapsed thread mode indicates if the current user is following this thread
 	Metadata     *PostMetadata `json:"metadata,omitempty" db:"-"`
 }
 
@@ -228,6 +229,7 @@ func (o *Post) ToUnsanitizedJson() string {
 }
 
 type GetPostsSinceOptions struct {
+	UserId                   string
 	ChannelId                string
 	Time                     int64
 	SkipFetchThreads         bool
@@ -236,6 +238,7 @@ type GetPostsSinceOptions struct {
 }
 
 type GetPostsOptions struct {
+	UserId                   string
 	ChannelId                string
 	PostId                   string
 	Page                     int