feat(fastify): add decorator for custom schema

[piotrfrankowski]

trafficstars

Add an ability to attach json schema to request with a RequestSchema decorator

PR Checklist

Please check if your PR fulfills the following requirements:

• [x] The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• [x] Tests for the changes have been added (for bug fixes / features)
• [x] Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• [ ] Bugfix
• [x] Feature
• [ ] Code style update (formatting, local variables)
• [ ] Refactoring (no functional changes, no api changes)
• [ ] Build related changes
• [ ] CI related changes
• [ ] Other... Please describe:

What is the current behavior?

Currently, there is no easy way of using fastify's schema property and adding a response schema can have positive impact on performance source

Issue Number: N/A

What is the new behavior?

This PR adds a new decorator RequestSchema that takes a schema object and sets it as schema property on fastify route doc

Does this PR introduce a breaking change?

• [ ] Yes
• [x] No

[coveralls]

Pull Request Test Coverage Report for Build 4564b87f-2f8f-4f0f-8778-fcf6b60673ff

Details

• 5 of 5 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.007%) to 88.93%

---

Totals
Change from base Build c493f148-f1dd-4b7d-a940-d13270fde234:	0.007%
Covered Lines:	7182
Relevant Lines:	8076

---

💛 - Coveralls

[jadejr]

This should include some documentation on how to use it.

[jadejr]

Oh, and it should have example usage in the fastify example.

[kamilmysliwiec]

LGTM