Enable configuring http(s) proxy for application capabilities CRDS

Operator application capabilities uses a HTTP client. For disconnected scenarios, the customer would want to use a HTTP(s) proxy. Currently it is only configurable using env vars (enabled in this PR). This is a workaround, though, because the customer is not expected to change the operator environment variables in the container.

The application capabilitites CRD's should provide a explicit way to support HTTP(s) proxies, only for the HTTP client connection to 3scale admin API. BTW, using env vars, all k8s API server traffic goes through the proxy as well, unless adding the k8s API service in the NO_PROXY env var.

The customer should be able to configure per custom resource:

• HTTP_PROXY
• HTTPS_PROXY
• NO_PROXY

Support for authenticated proxies also required.