perf: allow-list only needed files for packaging

[castarco]

In this small patch I add a short allowList to the package.json file, to ensure that only essential files are added to the distributed package.

• The package in its compressed form goes down from 3439 bytes to 2587 bytes (around 25% less)
• In its decompressed form, goes down from 22.4kB to 14.0kB (around 37% less)

It can be checked by running npm pack and inspecting the generated artifacts.

Signed-off-by: Andres Correa Casablanca castarco@coderspirit.xyz

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included (does not apply)
• documentation is changed or added (does not apply)
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[jsumners]

Thank you for your interest in this topic. Please see the discussion in fastify/skeleton#42 (comment) for my reasoning against such a change.