Hide HEAD routes by default

[mcollina]

This PR partially reverts https://github.com/fastify/fastify-swagger/pull/649 due to some unintended breakage. I had a couple of applications whose tests failed badly due to the HEAD routes now included in the definitions. This PR hides by default but add an option to expose them, both at the plugin level or at the route level. The plugin would rely anymore on the Fastify own settings.

Fixes #722

Checklist

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

[mcollina]

I would like to land this ASAP to avoid more breakages.