[enhancement]: Add option to download images in formats other than PNG

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Contact Details

_No response_

### What should this feature add?

When a user requests to download an image from Invoke's backend serve it in a more modern, possibly lossy, format (e.g. _webp_). It offers several benefits when later using these images in other environments: decreased storage requirements, faster upload times to cloud/social media platforms without sacrificing quality of generation.

Download of the original _png_ can be left as an option.

**Point of consideration**: when converting to another format, some/all metadata should be preserved to be able to trace back the image's origin.

### Alternatives

An alternative would be to convert the image into a desired format in post, i.e. manually.

### Additional Content

_No response_