Add additional fetch options

[OwenDelahoy]

Thank you for the fantastic library of JSON Web functions.

I have been trying to use jose-browser-runtime/jwks/remote inside Cloudflare workers
Although the code executes server side, the Cloudflare workers environment lacks many of node-js libraries. The environment is much more similar to a web worker running insider a browser.

Cloudflare provides a fetch function very similar to the standard fetch function, however Cloudflare's Request parameter lacks some of the properties in the standard Request parameter.

Unfortunately, if the user provides Request parameter options such as mode , credentials or referrerPolicy, then Cloudflare's fetch function will throw an error of the form

The 'mode' field on 'RequestInitializerDict' is not implemented.

Other libraries such as the aws sdk have encounter similar issues while being used inside cloudflare workers.
aws/aws-sdk-js-v3#1165

Currently these parameters are specified by the library and can not be configured.
https://github.com/panva/jose/blob/main/src/runtime/browser/fetch_jwks.ts#L15-L17

This pull request allows the user to configure/override these default parameters with undefined values, so that it can be used inside cloudflare workers.

[panva]

@OwenDelahoy thank you for bringing this up, I wasn't aware of CF workers specifics until now. I'm fine adding runtime specific options but, similar to Node.js's agent these should be a single parameter typed any documented to be fetch based runtime specific and not applicable to Node.js.

Thinking about it further it may be shared between runtimes and simply applied to both fetch() and http(s)(url, { ... options }), but it still be any as these are runtime specific options that the types cannot account for.

Let me make up my mind first, I don't want to open this up too much as to not allow myself the leeway of changing the implementation later. I do want to account for only the options that block you in CF workers as well, setting headers, allowing redirects, referrer or changing the method is not what i wish to support.

[panva]

How can one detect from e.g. globalThis that it is run in CloudFlare workers? Because if that's detectable I would just unset the properties that aren't implemented by CF.