Rename `ITK` repository default branch from `master` to `main`

[thewtex]

Description

main is now the default branch for GitHub projects as opposed to master. Provide the expected default.

Impact analysis

This will provide the expected default branch name, and it will also cause disruption to existing clones and forks.

Versions

Target for ITK 6.

Additional Information

Todo:

• [ ] Update related repositories
  • [ ] Update remote module's default branches (in progress)
  • [ ] Update ITKSphinxExamples
  • [ ] Update ITKSoftwareGuide
  • [x] Update ITK-Wasm
  • [x] Update itk-viewer
• [ ] Community notices (Discourse, etc.)
• [ ] https://adamj.eu/tech/2022/10/27/git-how-to-alias-master-as-main/
• [ ] Dashboard Scripts
• [ ] Scripts in the repository
• [ ] Release scripts
• [ ] Dashboard systems
• [ ] Setup nightly sync of master backwards compatibility branch to main
• [ ] Add to documentation how to update local clone configuration and GitHub forks
• [ ] GitHub Repository Settings Rename master default branch to main

@hjmjohnson

[github-actions[bot]]

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[dzenanz]

Welcome to the ITK community Matt 😄