Adding jf pip download command

[dortam888]

Is your feature request related to a problem? Please describe.
The Customer is using pip download to download python packages from the requirement.txt file and want to implement our jfrog cli in the pipeline

Describe the solution you'd like to see
Add the ability to use jf pip download same as jf rt dl but from python registry

Describe alternatives you've considered
You can use jf rt dl after installing the requirement.txt in Artifactory.