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

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

[reime005]

just (./CONTRIBUTING.md)

[Mookiies]

👍 changed to ./CONTRIBUTING.md

[github-actions]

🎉 This PR is included in version 6.2.2 🎉

The release is available on:

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

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