Enforce LF line endings for compose setup shell script (#128)

## What was changed

Enforced LF line endings for the `compose/scripts/setup-postgres-es.sh`
script via `.gitattributes`.

No changes to the script logic itself.

## Why?

Although the script is stored with LF line endings in the repository,
Git may check it out as CRLF on Windows due to `core.autocrlf`. When the
file is mounted into a Linux Docker container, this causes the POSIX
`/bin/sh` script to fail with:
```
set: illegal option -
```

Enforcing LF line endings at the Git level ensures the docker-compose
setup works reliably across platforms.

## Checklist

1. Closes #126 
2. How was this tested:
- Cloned the repository on Windows with `core.autocrlf=true`
- Ran the official docker-compose setup
- Verified that the setup script executes correctly inside the container
without `/bin/sh` errors

3. Any docs updates needed?
- No

---------

Co-authored-by: GeorgeSpring <GeorgeSpring@users.noreply.github.com>
Co-authored-by: alex.stanfield <13949480+chaptersix@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: 3 people

.gitattributes

@@ -0,0 +1 @@
+*.sh text eol=lf