fix: jwksUri should be optional when custom fetcher is provided

[cschetan77]

Description

Problem

Previously, the SDK required consumers to always provide a jwksUri, even when a custom fetcher was supplied. However, when a custom fetcher is used (which can retrieve keys from any endpoint), requiring jwksUri is unnecessary and restrictive. The current type definitions did not reflect this flexibility, forcing consumers to provide redundant configuration.

Solution

This PR updates the type definitions to accurately model the intended usage:

The Options type is now a union:

• When a fetcher is provided, jwksUri is optional.
• When a fetcher is not provided, jwksUri is required.

Because TypeScript interfaces cannot extend union types, the following types have been changed from interfaces to type aliases using intersections:

• ExpressJwtOptions
• HapiJwtOptions
• KoaJwtOptions

This change allows consumers to omit jwksUri when supplying a custom fetcher, improving developer experience and aligning the types with actual SDK behavior.

Potential Breakage

Since JwksRsa.Options has been changed from interface to type, if consumer tries to extend or implement Options, that will fail -

• interfaces cannot extend a union type, interface X extends JwksRsa.Options {}.
• classes cannot implement a union type.

References

#440

Testing

• If fetcher is provided, jwksUri is optional to pass and typescript compilation does not throw any error.