Build with download proxy and lib install proxy

[morya]

This question was first asked by me here: https://github.com/orgs/paketo-buildpacks/discussions/220

related question, https://github.com/orgs/paketo-buildpacks/discussions/51

But, I think this is a common need, and should be implemented in a general way.

What I encountered:
I can't build go code image, because network access is hard inside a air-gap environment.

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What I need:

• download dist from a mirror, like
  • download go1.20.9.linux-amd64.tar.gz
  • download node-18.xz
  • download python-3.10/ python-3.11.xz
• download common packages from mirror, like
  • install moment pkg from mirror instead of from official npm, ( maybe we are inside a company)
  • install tornado (python ilb) from mirror
  • install github.com/labstack/echo/v4 from mirror
• download pkg from a private git server
  • install a go get git.my-company.com/lib/encrypt from git.my-company.com, and with personal access token

There are no common way to define download proxy, private registry ( golang lib registry, node registry, pypi mirror)