Doc: Ensure LF line-endings

[geographika]

Ensure LF for cookbook doc.

Adds a new action to check for CRLF, configured to just check RST files.
There are 112 files with CRLF - see https://github.com/geographika/gdal/actions/runs/23262079608/job/67632989090.
Most are data or Windows-related files.

[dbaston]

Rather than adding another CI job, what about adding the following line to the existing "Lint .rst files" section of "doc_checks.yml" ?

if find . -name '*.rst' | xargs grep -P "\r$"; then echo 'Windows line breaks detected'; false; fi

[geographika]

@dbaston - I'll use that approach. Closing.