[MM-14588] Don't mark the channel as read when adding a member (#10680)

* add flag whether to mark channel as viewed for the requesting user

* remove marking channel as viewed when adding user to a channel

api4/channel.go

@@ -1182,7 +1182,7 @@ func addChannelMember(c *Context, w http.ResponseWriter, r *http.Request) {
 		}
 	}
 
-	cm, err := c.App.AddChannelMember(member.UserId, channel, c.App.Session.UserId, postRootId, c.App.Session.Id)
+	cm, err := c.App.AddChannelMember(member.UserId, channel, c.App.Session.UserId, postRootId)
 	if err != nil {
 		c.Err = err
 		return