Return group DN instead of group name in LDAP STS (#11501)

- Additionally, check if the user or their groups has a policy attached during
the STS call.

- Remove the group name attribute configuration value.

cmd/config/identity/ldap/legacy.go

@@ -41,10 +41,6 @@ func SetIdentityLDAP(s config.Config, ldapArgs Config) {
 			Key:   GroupSearchFilter,
 			Value: ldapArgs.GroupSearchFilter,
 		},
-		config.KV{
-			Key:   GroupNameAttribute,
-			Value: ldapArgs.GroupNameAttribute,
-		},
 		config.KV{
 			Key:   GroupSearchBaseDN,
 			Value: ldapArgs.GroupSearchBaseDistName,