chore: create .gitattributes（#2288）

It is recommended by Prettier to use LF endings for all files including in Windows, and they officially recommend to set this option in .gitattributes file for consistency, and LF is the default in Prettier 2 or higher. The lack of this file bit me in another project whose build failed in Windows in GitHub Actions due to `prettier --check` failing in Windows with default LF mode.

More info: https://github.com/prettier/prettier/issues/7825#issuecomment-602171740