proxy - add support to proxy svg images

[majorsilence]

• [x] Detect if a proxy url is an svg image
• [x] Cache the svg and serve it
• [x] Disable all image operations if the file is svg

ImageProxyRepo.cs will need to be modified to support generic file types that are unsupported by imagesharp. As an initial change, we will do an if statement. If the file is imagesharp supported use the existing functionality. If the file is not supported by imagesharp cache it and return it as is.