Limit the `request_format` to the default value set in the config

[pkarw]

Related: #486 Related: https://github.com/DivanteLtd/vue-storefront-api/pull/390/files

The goal of introducing the new query format was to make queyring Elastic safer. I mean we simply not let the users use full blown ElasticDSL anymore.

However, still the request_format can be overriden by the user and they can use Elastic DSL. We need to add to config a variable like allowedRequestFormats=search-query; limitRequestFormat=false and explicitly limit the queries that are running different formats in the catalog.js. The default value is false for the backward compatibility.