Document httpclient logging options

[chrisbetz]

Options:
-Djdk.httpclient.HttpClient.log=errors,requests,headers,frames[:control:data:window:all],content,ssl,trace,channel,all

Example:
-Djdk.httpclient.HttpClient.log=all

see

• https://medium.com/@kir.maxim/lesson-i-have-learned-from-using-jdk11-http-client-2cf990daba03
• https://stackoverflow.com/questions/53215038/how-to-log-request-response-using-java-net-http-httpclient