group member和friend request中添加extra字段

broker/migrate/h2/V39__add_group_member_friend_request_extra.sql

@@ -0,0 +1,2 @@
+alter table `t_group_member` add column `_extra` TEXT DEFAULT NULL;
+alter table `t_friend_request` add column `_extra` TEXT DEFAULT NULL;

broker/migrate/mysql/V44__add_group_member_friend_request_extra.sql

@@ -0,0 +1,2 @@
+alter table `t_group_member` add column `_extra` TEXT DEFAULT NULL;
+alter table `t_friend_request` add column `_extra` TEXT DEFAULT NULL;