Make studio file uploads site aware

[OmarIthawi]

This makes the assets API site-aware.

The assets API is what the File Page Upload uses.

This fixes: RED-147 - Itential: Make Files & Uploads web links microsite-aware.

[johnbaldwin]

LGTM!

[johnbaldwin]

Cool!

[johnbaldwin]

@OmarIthawi Do we need to check that asset_url has a leading slash? I assume asset_url is the resource path from the root?

[OmarIthawi]

Great question @johnbaldwin!

Yes, I think we do need it. I want to avoid the http->https redirect which Open edX enforces by default. The double slashes ensure that at least when a secure site uses the URL, it'll work.

The leading slashes break the link for when including the files in an on-disk HTML file (file://) but we don't care about this case.

Some annoyance is found when using $ curl:

$ curl //courses.edx.org/robots.txt
curl: (3) <url> malformed

I do like to have the leading slashes, but I'm open to removing them.

I've also renamed base to be domain so it's more clear, and yes asset_url looks like the following: /asset-v1:Red+Red+Red2020+type@asset+block@2017-Scrum-Guide-US.pdf

[OmarIthawi]

Thanks @johnbaldwin! I've answered your comments. I'll merge for now. Let me know if this would need a follow up work!