Feature request: Fetch spec from URL

[soofstad]

Hi, awesome tool 👍

Would it be possible to implement a feature where the OpenApi spec where fetched from URL?

For example; I'm using FastAPI for my API, which has an integrated spec generator that is served at /openapi.json.
It's easy enough to curl this url, save to a file, and run the tool as usual. But just being able to do; openapi-fuzzer --spec http://localhost/openapi.json would be nice.