Move createError utility to its own package

[delvedor]

As titled, the idea is to offer a simple and consistent way to plugin author for creating error objects.
The idea started from fastify/under-pressure#54 (comment).

I'm thinking to extract our warnings utility in the same external module as well, so plugin authors could use the same mechanism for emitting warnings.
You can find the extracted module here.

Feedback?

TODO:

• Update typescript types
• Update documentation

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 Code of conduct

[jsumners]

LGTM

[mcollina]

Code's ok, doc is missing.

[Ethan-Arrowood]

lgtm checking out fastify-error now

[delvedor]

@mcollina @jsumners @Ethan-Arrowood how do you feel about moving in that module our warnings utility as well?
We could export it as a separate module as well.

[jsumners]

I'd see it as a separate module. Maybe fastify-deprecation or something. Keep to the "do one thing and do it well" model.

[mcollina]

lgtm

[github-actions]

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