Implement CreateGroup support for Graph LDAP Backend

This add basic support to create Groups in LDAP via the GraphAPI.
Currently this is hardcoded to use the standard LDAP "groupOfNames"
objectClass.

graph/pkg/identity/backend.go

@@ -21,6 +21,8 @@ type Backend interface {
 	GetUser(ctx context.Context, nameOrID string) (*libregraph.User, error)
 	GetUsers(ctx context.Context, queryParam url.Values) ([]*libregraph.User, error)
 
+	// Create Group creates the supplied group in the identity backend.
+	CreateGroup(ctx context.Context, group libregraph.Group) (*libregraph.Group, error)
 	GetGroup(ctx context.Context, nameOrID string) (*libregraph.Group, error)
 	GetGroups(ctx context.Context, queryParam url.Values) ([]*libregraph.Group, error)
 }