Enable proxy environment variables via the APICAST CRD

The apicast CRD does not handle proxy or no_proxy environment variable. The only workaround to enable this is to scale down the operator like below:

oc scale deployment apicast-operator --replicas 0
oc set env deployment apicast-example-apicast HTTP_PROXY=http://example.org:80

The expected parameters to be supported are the following:

http_proxy
https_proxy
no_proxy
all_proxy

as described in the following doc reference

https://github.com/3scale/APIcast/blob/master/doc/parameters.md