Fix add listener types

[Mookiies]

Summary

Fix TypeScript types for the addListener method for two scenarios:

1: addListener supports a null uploadId to include all uploads. 2: return type is EventSubscription not void

Adds "@types/react-native": "^0.64.x" as a devDependency to get correct types for EventSubscription.

Examples of where these incorrect types causes issues:

1: Want to call addListener with null but get a typescript error

// TS error: Argument of type 'null' is not assignable to parameter of type 'string'. 
Upload.addListener('cancelled', null, () => {})

2: In an instance where a reference to the returned EventSubscription is desired a unsafe typecast workaround is required to get to the correct typing. Current situation:

const subscription = (Upload.addListener('progress', uploadId, (response) => {
    ...
}) as unknown) as EventSubscription;

After fix:

const subscription = Upload.addListener('progress', uploadId, (response) => {...});

Also fixes link to the contributing doc from readme.

Test Plan

Verify addListener works as expected with updated types

Compatibility

OS	Implemented
iOS	✅
Android	✅

Checklist

• [x] I have tested this on a device and a simulator
• [ ] I added the documentation in README.md
• [x] I updated the typed files (TS and Flow)
• [ ] I've added Detox End-to-End Test(s)

[github-actions[bot]]

:tada: This PR is included in version 6.2.2 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot :package::rocket: