feat: allow optional response status code validation

[sceccotti89]

Checklist

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

[mcollina]

Can you please fix the linting?

[sceccotti89]

@mcollina Fixed.

[mcollina]

Can you please add a test for the type https://github.com/fastify/fastify-response-validation/blob/master/types/index.test-d.ts?

[sceccotti89]

@mcollina Thanks for the feedback. Test added.

[sceccotti89]

My last forced push commit was to solve the linting issue. It should all be fine now.

[sceccotti89]

@Uzlopak PR updated.

[sceccotti89]

Hi guys. Any chance this can get merged soon?