API versions & backends

adds v2 to swagger petstore API
adds v3 to swagger petstore API
adds backend for swagger petstore
sets swagger petstore backend for each API version via set-backend-service policy
adds overrides for apis in production environment
updates README

Versions have no issue deploying, see revision issues at https://github.com/Azure/apiops/issues?q=is%3Aissue+is%3Aopen+revision

I bumped the version of the publisher after speaking with the API Ops folks but that did not fix the problem so the revision that had been added has been removed for now.

lucashuet93 / apiops-vnet-github

API versions & backends #28