feat(express): Introduce Clerk package for Express

[dimkl]

Description

Introduce Express specific Clerk SDK @clerk/express. The SDK exposes the following API:

• clerkClient: default @clerk/backend client initialized from env variables and used to make BAPI requests
• clerkMiddleware: centralized middleware that authenticates all requests without blocking them (also triggers handshake mechanism)
• getAuth: utility to retrieve the auth state from the request (requires clerkMiddleware to executed)
• requireAuth: middleware that returns http 401 response when request is signed-out

Also all the top level exports from @clerk/backend are re-exported from @clerk/express top level.

Checklist

• [ ] npm test runs as expected.
• [ ] npm run build runs as expected.
• [ ] (If applicable) JSDoc comments have been added or updated for any package exports
• [ ] (If applicable) Documentation has been updated

Type of change

• [ ] 🐛 Bug fix
• [x] 🌟 New feature
• [ ] 🔨 Breaking change
• [ ] 📖 Refactoring / dependency upgrade / documentation
• [ ] other:

TODOs

• [x] Add tests
• [ ] Add examples
• [x] Replace all TODO(express) TODOs
• [ ] Use this package to create separate page in backend-request/handling docs

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: 55d9b64d3dda2563ba4de99e07c1a7707389492f

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@clerk/express	Patch

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[dimkl]

@LekoArts, @nikosdouvlis Could you take another look at this PR?