chore: drop Node.js 14 and lower

[dhmlau]

BREAKING CHANGE: drop support for Node.js 14 version and lower

Checklist

• [x] Sign off your commits with DCO (Developer Certificate of Origin)
• [x] npm test passes on your machine
• [ ] New tests added or existing tests modified to cover all changes
• [x] Code conforms with the style guide
• [x] Commit messages are following our guidelines

[dhmlau]

@achrinza, would upgrading typescript typedefs be breaking change too?