refactor(looker): streamline handling of dimension group fields in view upstream processing

- Updated logic to ensure only one field per dimension group is added, improving clarity and maintainability of the code.
- Removed redundant checks and added comments for better understanding of the dimension group handling process.

Author: askumar27

metadata-ingestion/src/datahub/ingestion/source/looker/view_upstream.py

@@ -622,17 +622,15 @@ def _get_fields_from_looker_api(self, explore_name: str) -> List[str]:
                         if dim_field.name and self._is_field_from_current_view(
                             dim_field, current_view_name
                         ):
-                            # Skipping adding dimension group fields if already added
-                            if (
-                                dim_field.dimension_group
-                                and dim_field.dimension_group
-                                in dimension_group_fields_mapping
-                            ):
-                                continue
-                            else:
-                                assert (
-                                    dim_field.dimension_group is not None
-                                )  # HAPPY linter
+                            # Handle dimension group fields - only add one field per dimension group
+                            if dim_field.dimension_group:
+                                # Skip if this dimension group already has a field
+                                if (
+                                    dim_field.dimension_group
+                                    in dimension_group_fields_mapping
+                                ):
+                                    continue
+                                # Add this field as the representative for this dimension group
                                 dimension_group_fields_mapping[
                                     dim_field.dimension_group
                                 ] = dim_field.name