graph: Allow provisioning users with legacy names (#5255)

Via configuration you can now configure to skip the validation of username and
instead decide to trust the upstream system that is adding users.

services/graph/pkg/config/defaults/defaultconfig.go

@@ -36,6 +36,7 @@ func DefaultConfig() *config.Config {
 		},
 		API: config.API{
 			GroupMembersPatchLimit: 20,
+			UsernameMatch:          "default",
 		},
 		Reva: shared.DefaultRevaConfig(),
 		Spaces: config.Spaces{