feat: add proxy authentication to schema registry

[tiboun]

Add new property for schema registry (proxy.user and proxy.password) in order to authenticate with proxy requiring authentication. The authentication rely on Authenticator which is globally set and configuration of the RestService will be a replace of the globally set configuration.

http proxy with authentication has been disabled by default since JDK8.111 and in order to reach https, system property must be set to empty :

• jdk.http.auth.tunneling.disabledSchemes
• jdk.http.auth.proxying.disabledSchemes

System.setProperty("jdk.http.auth.tunneling.disabledSchemes", "");
System.setProperty("jdk.http.auth.proxying.disabledSchemes", "");

This code has been tested by using fiddler has a proxy with authentication requirement and by using HttpURLConnection with my corporate network with the same Authenticator code.

No unit tests has been written though. I'm waiting for an answer of mock-service. See #2137. This PR close #2137.

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