Support for pip download

[g3n35i5]

Is your feature request related to a problem? Please describe.
In my (jenkins) pipeline, I'd like to download pip packages from Artifactory and I'd like to do this with the help of the the jenkins artifactory plugin.

Describe the solution you'd like to see
There could be a new method download in PipDriver. This would then have to be propagated through to the Jenkins Artifactory plugin via a suitable binding:

• New class PipDownload.java with basically the same functionality as PipInstall.java
• In the jenkins artifactory plugin a new PipInstallExecutor with basically the same functionality as PipDownloadExecutor
• In the jenkins artifactory plugin a new method download in the class PipBuild.java which then calls the underlying download method

Describe alternatives you've considered
You could simply specify the Artifactory PyPi server as index for a "plain" pip download command. But then the downloaded artifacts don't show up in the buildInfo.

Additional context
N/A