Upgrade to latest LTS version of Node.js

[nilsnh]

Problem:

Node.js LTS 14 will stop getting security updates next year. So, we should move to the next LTS release. See: https://nodejs.org/en/about/releases/

Steps to fix:

• Change netlify.toml from NODE_VERSION = "14.18.0" to NODE_VERSION = "lts/*" which would make NVM grab latest LTS release. See: https://docs.netlify.com/configure-builds/manage-dependencies/#node-js-and-javascript
• Remove AWS_LAMBDA_JS_RUNTIME = "nodejs14.x" which would make Netlify functions just use the latest LTS release.
• Update package.json to require at least Node v16 version for local development.
• Once we have a pull request for this, we must check that everything still builds and functionality works correctly.