MK8S-25: Fix nginx root directory access with index.html

Add nginx root directory (/var/www/repositories/) to index.html creation
for scality repository. This fixes the error:
"directory index of /var/www/repositories/ is forbidden"

The health check and nginx now have proper index.html files at all levels:
- /var/www/repositories/index.html (nginx root)
- /var/www/repositories/metalk8s-131.0.0-dev/index.html (saltenv root)
- Repository-specific index.html files

This ensures nginx can serve directory requests when autoindex is disabled.

Author: rdebay-scality

buildchain/buildchain/targets/repository.py

@@ -252,6 +252,10 @@ def _get_repository_directories(self) -> List[Path]:
             self.rootdir / self.ARCH,  # Architecture directory (e.g., x86_64)
         ]
 
+        # Add nginx root directory for scality repository
+        if self.name == "scality":
+            repository_directories.append(self._repo_root)  # /var/www/repositories
+
         # Add saltenv directories for scality repository
         saltenv_dir, top_saltenv_dir = self._get_saltenv_directories()
         if saltenv_dir and top_saltenv_dir: