Should allow for proxy configuration

[AndreasSM]

logevents/logevents/src/main/java/org/logevents/observers/HttpPostJsonLogEventObserver.java

Line 19 in 1f368c1

 public HttpPostJsonLogEventObserver(URL url) { 

Sometimes your server is required to og via a Proxy when you post messges to i.e slack or teams

Expected behaviour:
Observer can be configured with proxyhost and proxyport. Configuration is passed to HttpPostJsonLogEventObserver as url Properties and ultimately added to the http request