Support Node 20

[bestbeforetoday]

As a Node application developer I want to build and run my application with Node 20 So that I can stay current with latest features and bug fixes

Node 20 is scheduled to become an LTS release on 2023-10-24. Once available, the following tasks are required:

• [x] Add Node 20 to GitHub Actions test matrix
• [x] Use Node 20 as the default Node version for version-agnostic GitHub Actions workflows
• [x] Either on next release or if no code changes are required to pass tests, update documentation to include Node 20 in compatibility matrix.