Install packages without redirect

[janjagusch]

When inspecting a package download from Quetz (mamba install --verbose), we've noticed that Quetz doesn't return the package file directly. Instead, it redirects to the underlying storage layer, like GCP or S3.

Example from our logs:

info     libmamba Transfer done for 'mypackage'
info     libmamba Transfer finalized, status: 200 [https://storage.googleapis.com/mybucket/noarch/mypackage-1.0.0-py_0.tar.bz2...]

This is problematic for us, as we work in restricted infrastructure, where Google (and many other) domains tend to be blocked. It would be really useful to us if Quetz returned the package file itself, instead of returning a pre-signed URL to a Cloud provider.

We would be happy to contribute this feature, maybe as a form of server or channel-specific configuration, to Quetz. But before that, it would be appreciated if you could point us in the right direction, as we're not entirely sure which Quetz route is called when Mamba tries to fetch a package.

[jonashaag]

You might want to have a look at #506 where I started implementing the opposite for repodata.json. Without #506 repodata.json is always streamed to the client. You may want to reuse some of the related logic to enable streaming for package data as well.