[Enhancement] Be able to load custom --index-url packages from configuration file to python-inspector

[qequ]

Currently python-inspector can't find custom packages loaded from --index-url.
When having private packages that pip can load via --index-url, ort should be able to find them via ort's configuration file

CC: @arieltorti @dgutson

[sschuberth]

Probably related to aboutcode-org/python-inspector#11.

[sschuberth]

Let's track this in the above-mentioned python-inspector issue only.

[dgutson]

@arieltorti is this a misunderstanding? Please clarify. I think this is an ORT issue.