Add global variable for accessing the proxy settings in pipelines

[coder-hugo]

I haven't found any existing solution for this and I also haven't got an answer for my question in the jenkins-users group. Therefore I just implemented a global variable that provides access to the Jenkins proxy settings in pipelines. I think this plugin is a good place for such a variable. But if you are thinking differently I can move this also to a separate plugin.

[coder-hugo]

I just changed my PR according to your suggestion. There is now a step (withHttpProxyEnv) that provides the global proxy settings as the following environment variables:

• http_proxy/HTTP_PROXY
• https_proxy/HTTPS_PROXY
• no_proxy/NO_PROXY

I add both the lower case and the upper case format as there are commands that like just the lower case format and others that just like the upper case one.

[shiranhonigFiverr]

Hello, Is this fix about to be merged? is there another solution for this problem? Thanks!