Provide a way to prevent getKeysInterceptor falling back to jwksUri when the result doesn't contain the kid

[sam-super]

Checklist

• I have looked into the Readme and Examples, and have not found a suitable solution or answer.
• I have searched the issues and have not found a suitable solution or answer.
• I have searched the Auth0 Community forums and have not found a suitable solution or answer.
• I agree to the terms within the Auth0 Code of Conduct.

Describe the problem you'd like to have solved

I have a service which issues a jwt, but also validates a token it has issued (on a separate request).
I want to provide the jwk from the filesystem (rather than a uri, since the key is already in the service).
I also have multiple auth strategies (meaning upstream issuers).
However, if the provided kid isn't in the response from getKeysInterceptor, it will fall back to the uri.
Since i have multiple strategies, it's normal that an auth token will contain a kid that doesn't exist for one of my strategies.

Describe the ideal solution

Ideally (for the stated use case), there would be no fallback, and i would have the option to supply a function OR a uri to jwksUri in order to load the correct jwk.

This would cause issues with existing consumers who rely on the fallback, so some other more pragmatic options:

1. allow jwksUri to be a function (as well as a string), and if it's a function, execute it in a similar way to how getKeysInterceptor currently works (the existing getKeysInterceptor function still exists and falls back to jwksUri, which is a bit confusing).
2. add another boolean option jwksUriFallback which defaults to true to maintain current functionality (this is the simplest option but makes the config confusing: setting the jwksUri is mandatory but will never be used).
3. make jwksUri OR getKeysInterceptor be required (rather than jwksUri being required). If jwksUri is not set, don't fall back.

Alternatives and current workarounds

No response

Additional context

The existing code looks good so I'm happy to put together a PR implement the chosen solution.

[sam-super]

fwiw i think option 3 is the best:

3. make jwksUri OR getKeysInterceptor be required (rather than jwksUri being required). If jwksUri is not set, don't fall back.

[sam-super]

I put this PR up just because i had already done it the jwksUriFallback boolean way for my specific case:
#389
but happy to change to whataever