MM-45120: Track team join times. Add API to retrieve new team members since a given time. (#20708)

* MM-45120: Starts tracking team join time. Adds API to retrieve team members who joined after a given time.

* MM-45120: Updates json casing to match model.User.

store/sqlstore/user_store.go

@@ -1765,7 +1765,7 @@ func (us SqlUserStore) GetUsersBatchForIndexing(startTime int64, startFileID str
 
 	teamMembers := []*model.TeamMember{}
 	teamMembersQuery, args, _ := us.getQueryBuilder().
-		Select("TeamId, UserId, Roles, DeleteAt, (SchemeGuest IS NOT NULL AND SchemeGuest) as SchemeGuest, SchemeUser, SchemeAdmin").
+		Select("TeamId, UserId, Roles, DeleteAt, CreateAt, (SchemeGuest IS NOT NULL AND SchemeGuest) as SchemeGuest, SchemeUser, SchemeAdmin").
 		From("TeamMembers").
 		Where(sq.Eq{"UserId": userIds, "DeleteAt": 0}).
 		ToSql()