* ci: `.gitattributes` - Ensure `eol=lf` for shell scripts
- These files should always use LF for line endings during a checkout.
- `Dockerfile` does not like building with HereDoc `RUN` scripts that expect LF.
* chore: Use `.yml` extension
Both of these files support the `.yml` extension. Normalize on that.
* fix: Add `.gitattributes` to ensure `LF` line-endings are committed
Avoids accidentally committing files with `CRLF` when they're created on Windows. Or worse, if some editors don't detect `LF` and would introduce mixed line-endings with `CRLF`.
Shouldn't be a problem in practice as we already have a linting check to catch this via CI during PRs. This file is complimentary, in that it should automate that concern away.