docs(sql): Clarify that get_primary_keys returns column names, not values

- Updated docstring to specify 'primary key column names' instead of just 'primary keys'
- Added Returns section explaining the method returns column names or None
- Addresses @dbgold17's clarifying question about terminology in GitHub comment

Co-Authored-By: AJ Steers <[email protected]>

Author: devin-ai-integration[bot]

airbyte_cdk/sql/shared/catalog_providers.py

@@ -120,11 +120,14 @@ def get_primary_keys(
         self,
         stream_name: str,
     ) -> list[str] | None:
-        """Return the primary keys for the given stream.
+        """Return the primary key column names for the given stream.
 
         We return `source_defined_primary_key` if set, or `primary_key` otherwise. If both are set,
         we assume they should not should differ, since Airbyte data integrity constraints do not
         permit overruling a source's pre-defined primary keys. If neither is set, we return `None`.
+        
+        Returns:
+            A list of column names that constitute the primary key, or None if no primary key is defined.
         """
         configured_stream = self.get_configured_stream_info(stream_name)
         pks = configured_stream.stream.source_defined_primary_key or configured_stream.primary_key