types: export FastifyHelmetOptions to TypeScript users

[sniperwolf]

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

[coveralls]

Pull Request Test Coverage Report for Build 1672290443

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 1598031313:	0.0%
Covered Lines:	26
Relevant Lines:	26

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 1671986596

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

---

Totals
Change from base Build 1598031313:	0.0%
Covered Lines:	26
Relevant Lines:	26

---

💛 - Coveralls

[darkgl0w]

Thank you for your contribution ^_^
Can you please add a test inside the index.test-d.ts file ?

[sniperwolf]

@darkgl0w Something like the following make sense as a test to prove that fastify-helmet instance is using the 
FastifyHelmetOptions options?

expectType<FastifyPluginCallback<FastifyHelmetOptions> & {
    contentSecurityPolicy: typeof helmet.contentSecurityPolicy;
}>(fastifyHelmet);

[darkgl0w]

Yes something like this should be enough.

Seen that we export FastifyHelmetOptions we can do something like this too :

const helmetOptions = {
  contentSecurityPolicy: false,
  dnsPrefetchControl: false,
  expectCt: false,
  frameguard: false,
  hidePoweredBy: false,
  hsts: false,
  ieNoOpen: false,
  noSniff: false,
  permittedCrossDomainPolicies: false,
  referrerPolicy: false,
  xssFilter: false
}

// or maybe: expectAssignable<FastifyHelmetOptions>(helmetOptions);
expectType<FastifyHelmetOptions>(helmetOptions);

[mcollina]

Can you please add a unit test?

[darkgl0w]

LGTM