Deprecate proxyAuthorization

[shawkins]

Supporting raw proxyAuthorization values basically only works across all http clients with http proxy servers and http endpoints. It does not work for socks proxies, or for https endpoints with vertx and jetty (recent changes will allow that to work for basic auth specifically). This was initially brought up in the discussion around #6352

The steps would be:

• initially support proxyAuthorization, but only if it is http basic and add another method or methods such as proxyCredentials/Username/Password
• later remove support entirely for proxyAuthorization