[CCV-4649] Move RelationshipTool under common labelbox import (#1997)

Author: kjamrozy

libs/labelbox/src/labelbox/__init__.py

@@ -54,6 +54,7 @@
 from labelbox.schema.tool_building.fact_checking_tool import FactCheckingTool
 from labelbox.schema.tool_building.step_reasoning_tool import StepReasoningTool
 from labelbox.schema.tool_building.prompt_issue_tool import PromptIssueTool
+from labelbox.schema.tool_building.relationship_tool import RelationshipTool
 from labelbox.schema.role import Role, ProjectRole
 from labelbox.schema.invite import Invite, InviteLimit
 from labelbox.schema.data_row_metadata import (