Feature: support stable horde r2 upload

[MaikoTan]

Scope

Others

Describe the problem related to the feature request

Currently r2 upload feature is marked as default on stable horde, so we now need to support this.

The r2 upload feature basically changed the original generations.*.img from a base64 string to a cloudflare storage URL, so we need to request that URL before sending the image to an adapter.

Describe the solution you'd like

change return generations[0].img to return ctx.http.axios(generations[0].img) (maybe need some if-check)

Describe alternatives you've considered

Nay

Additional context

Thank you, Maiko.