gitattributes: ensure all text files end with LF

[radeksimko]

This is in preparation for automating marketplace publishing, which will run on GitHub-hosted Windows instance.

The original configuration has a few problems:

• every file is treated as text (including files which should be treated as binaries)
• some binary files have their line endings converted after checkout on Windows, which then prevents publishing

Run npx -- vsce publish 2.14.1
 ERROR  Command failed: npm version 2.14.1
npm ERR! Git working directory not clean.
npm ERR! M terraform-banner.png
npm ERR! M terraform.png

npm ERR! A complete log of this run can be found in:
npm ERR!     C:\npm\cache\_logs\2021-09-15T07_53_35_881Z-debug.log

[jpogran]

👍🏼 Explicit is always better than implicit!

[github-actions]

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