Exposes flavor extra_specs in the flavor representation since
microversion 2.61. Now users can see the flavor extra-specs
in flavor APIs response only and do not need to call
``GET /flavors/{flavor_id}/extra_specs`` API.
Flavor extra_specs will be included in Response body of the
following APIs:
* ``GET /flavors/detail``
* ``GET /flavors/{flavor_id}``
* ``POST /flavors``
* ``PUT /flavors/{flavor_id}``
Part of blueprint add-extra-specs-to-flavor-list
Change-Id: I048747633babf690a63c6de9773bff5547872053