Add server groups quota attributes in limit schema

If 'os-server-group-quotas' extension is enabled then,
absolute_limits GET API's response includes 'maxServerGroupMembers',
'maxServerGroups' and 'totalServerGroupsUsed' attributes too.

This patch adds those attributes in schema files.

Change-Id: I0d7adbdfe295d6cd27a8cb944fbaee3681113c42
1 file changed