[MM-23651] No more than 256 members are allowed to be invited (#15414)

* Update constant to 256

* update test

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

api4/team.go

@@ -20,7 +20,7 @@ import (
 )
 
 const (
-	MAX_ADD_MEMBERS_BATCH    = 20
+	MAX_ADD_MEMBERS_BATCH    = 256
 	MAXIMUM_BULK_IMPORT_SIZE = 10 * 1024 * 1024
 	groupIDsParamPattern     = "[^a-zA-Z0-9,]*"
 )