Upgrade to NPM 8.1

[ryantrem]

Describe the change

GitHub build agents upgraded the node version and now use NPM 8.1. This change upgrades this repo to use NPM 8.1 as well. The biggest parts of this change are:

1. Package lock file format version 2 - the lock files look much different now and aren't easily diff'd with the previous version.
2. NPM 7+ auto installs peer dependencies, so these need to be filtered out of the metro bundler when pulling in sym linked dependencies to Playground (e.g. the BRN module).

Screenshots

N/A

Documentation

Updated the readme to callout the new version of Node.js that should be used (which includes NPM 8.1).

Testing

Tested on iOS and Android. It seems unlikely it would be fine on those two platforms and not Windows, but I'm not 100% sure.
Also tested a local build of the BRN npm package on Android.