feat: csp nonce generation

[climba03003]

Resolve: #89

This PR aims to simplify the usage for csp nonce generation with fastify and helmet.

Changes:

• introduce new option enableCSPNonces
• decorate FastifyReply with cspNonce

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 623488680

• 0 of 17 (100.0%) changed or added relevant lines in 1 file 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 620283465:	0.0%
Covered Lines:	25
Relevant Lines:	25

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 623488680

• 17 of 17 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

---

Totals
Change from base Build 620283465:	0.0%
Covered Lines:	25
Relevant Lines:	25

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 624002530

• 17 of 17 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

---

Totals
Change from base Build 620283465:	0.0%
Covered Lines:	25
Relevant Lines:	25

---

💛 - Coveralls

[climba03003]

Opps, missed this comment #90 (comment)
I think this is more like the fastify style of csp nonce generation.

[mcollina]

Please move the generation of this middleware outside of the hook.

[climba03003]

I think it is a must for this middleware to exist inside the hook. As we are not passing the function inside helmet.
The options for helmet.contentSecurityPolicy is unique for every calls.

[mcollina]

lgtm

[mcollina]

Go ahead and merge & release this!