Add .gitattributes file

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Pull request description

This overrides user based core.autocrlf setting and ensure all staged files line endings are normalized.

This ensures only LF terminated lines in text files end up in the repository.

Relevant:

• https://git-scm.com/docs/gitattributes#_text
• https://docs.github.com/en/get-started/getting-started-with-git/configuring-git-to-handle-line-endings#per-repository-settings

PR meta checklist

• [X] Pull request is targeted at main branch for code
• [ ] Pull request is linked to all related issues, if any.

Code PR specific checklist

• [ ] My code follows the code style of this project and AspNetCore coding guidelines.
• [ ] My change requires a change to the documentation.
  • [ ] I have updated the documentation accordingly.
• [ ] I have updated the appropriate sub section in the CHANGELOG.md.
• [ ] I have added, updated or removed tests to according to my changes.
  • [ ] All tests passed.