Updated to Fastify v4, dropped error handler

[mcollina]

Signed-off-by: Matteo Collina hello@matteocollina.com

This PR updates to Fastify v4 and drops the custom error handler support.
I do not think that's needed with Fastify v4 by default as that's now way simpler to manage.

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[hsynlms]

May I ask for the details of dropping the custom error handler?
I wonder what Fastify v4 gives us different than v3 to achieve the same motivation.

The motivation was:

This plugins also adds a custom error handler, which hides the error message in case of 500 errors that are being generated by throwed errors, instead it returns Something went wrong.

[hsynlms]

@mcollina details?

[mcollina]

Check out fastify/fastify#3261