Add TypeScript types for key generation functions

[mahmoud-moursy]

Sorry for not creating a discussion first -- alas, I read the CONTRIBUTING.md just after finishing up the code for this contribution.

Benefits

• It's simply more convenient (for us puny humans, at least) to have autocomplete for the accepted algorithms.
• Protects against potential typos, which may cause runtime crashes, by providing a type error.
• I expect that this change is NOT breaking, because using an invalid algorithm causes a runtime crash anyway.

Costs

The weakest link in any cybersecurity system is humans; there is a danger that, by introducing automatic type hints, users may potentially do less pre-reading before using Jose and accidentally introduce security vulnerabilities into their own code-bases by using inappropriate algorithms. I have tried to link to the relevant documentation in the JSDoc comments of these types to reduce the incidence rate of this.

Tests(?)

I made sure to run npm format and npm test before contributing this. Nothing seems broken from what I can glean.

AI Disclosure

All the code was written by hand. I submitted it to Claude to review, where it did catch a typo that I'd made in the identifier for the type SecretKeyAlgorithm.

[mahmoud-moursy]

@panva sorry for pinging you about this -- not sure if you have notifications for pull requests turned on or not.