Add typescript definitions

[simoneromano96]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the feature has not already been requested

🚀 Feature Proposal

Add typescript definitions for use in typescript projects

Motivation

I'm currently using fastify-caching in a typescript project, however there are no type definitions so typescript goes in error.
Note that the abstract-cache library suffers from the same issue.

Example

import fastifyCaching from "fastify-caching"

Could not find a declaration file for module 'fastify-caching'. '/[**REDACTED**]/node_modules/fastify-caching/plugin.js' implicitly has an 'any' type.
  Try `npm i --save-dev @types/fastify-caching` if it exists or add a new declaration (.d.ts) file containing `declare module 'fastify-caching';`ts(7016)

[darkgl0w]

Hello !
Would you like to send a Pull Request to address this issue? Remember to add unit tests.

[Aslam-13]

Hi,
I have look into the issue but did not understand how to add that declaration can you pls help me. Pls assign to me as well.

[mcollina]

You can take a look at fastify-static or fastify-jwt for examples.