Add custom download URL

[etiennebonnafoux]

Description

I add a cli option in the download command to specify a custom url. This is usefuls for people in air gapped environment that should download models from mirror.

Types of change

It is a small enhancement

Checklist

• I confirm that I have the right to submit this contribution under the project's MIT license.
• I ran the tests, and all new and existing tests passed.
• My changes don't require a change to the documentation, or if they do, I've added all required information.

[etiennebonnafoux]

WIP, I have to write documentation and run the tests.

[etiennebonnafoux]

• I ran the tests, and all new and existing tests passed.

[etiennebonnafoux]

• I've added all required information in documentation