Derivation_url: allow adding an URL "file extension"

For now, derivation_url if generated ending with the file obejct serialized.
This makes a long URL fore sure, but it works.
When using some CDN solution like Cloudflare, only some “file extensions” are being cached, otherwise we have to define a specific Page Rule to force caching of some URLs.
I’d like to have URLs generated with a pseudo-file-extension ending, based on the file’s content-type, which would look more natural to users and to Cloudflare, too.
Any idea ?

Thank you !

At the moment this isn’t possible OOTB, though you could probably add the extension manually to the derivation URL, then wrap Shrine.derivation_endpoint into a middleware that strips the URL extension away before the request is passed to the derivation endpoint.

I would accept a pull request that adds this feature.