Upgrade supported node version

[peterthehan]

Proposed Changes

• Update readme and package indicating Nodejs 14.x LTS is the version that the package supports
• Update GitHub Action workflows to use 14.x
• Addresses Investigate & Upgrade Supported Node Version #21

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)

Test Plan and Documentation

Verified build passes

[finn-orsini]

As per offline discussion, going to hold off on merging this in case we want to cut a release before a major but otherwise accepted 👍