[Feature]: Allow customizing melpa archive.json location

[noctuid]

Feature Description

Our firewall blocks melpa. Not sure if this edge case warrants allowing it to be customizable, but I'd rather do that than continue to override the internal function.

Confirmation

• [x] The feature I'm proposing does not already exist in Elpaca

[progfolio]

Where do you pull the metadata from?

[noctuid]

For now I just downloaded the file on another computer and uploaded it as a gist and used that url. I guess it would also be nice if you could point it at a local file so I could just clone melpa and use make json.

[progfolio]

Another option would be to store elpaca/cache/melpa.eld in a gist and sync that to your work machine.