Expose setting/environment variable for maximum response size

[Sircrab]

When trying to download URLs through some of the plugins, certain galleries exceed the maximum default size for responses set by Mojolicious which causes the job to fail. While this default size is useful for most cases, it'd be great to have this exposed as an environment variable (or setting). The download_url method in the Upload model seems like a good place to check and update this setting to the user agent that gets the gallery.

[Difegue]

huh, I didn't think anyone would hit the 2GB response size limit, but I guess that can happen.
I'm not sure it's worth making this a setting, for downloads we can probably just bump it up to an obscene maximum size like 2TB.