Rename the main development branch from master to main

[willklein]

⚡️ Improvement

master => main. Let's make the switch post major release.

Motivation

Move from an antiquated and even harmful term to something more semantically meaningful. master is at best jargon-based, and newer developers going forward will be more and more accustomed to main.

Example

main is now the default branch for new repos on GitHub github/renaming (guidance)

Todo

• [ ] Investigate how this changes forked repos
• [ ] Catalog CI configuration to update
• [ ] Catalog references in the repo
• [ ] Update Canvas Kit Actions to be version 2
• [ ] Investigate how any design site links may break
• [ ] Update in-flight PRs
• [ ] Notify everyone in our internal Slack
• [ ] Communication for GH community
• [ ] Update all docs

[jaclynjessup]

Open question - What happens with everyones forked repo?