feat(tools): create enterprise_web_search_tool as a tool instance

There is no argument for the tool, so just like google_search, we should make it an easy-to-use tool instance.

PiperOrigin-RevId: 791266806

src/google/adk/tools/__init__.py

@@ -17,6 +17,7 @@ from ..auth.auth_tool import AuthToolArguments
 from .agent_tool import AgentTool
 from .apihub_tool.apihub_toolset import APIHubToolset
 from .base_tool import BaseTool
+from .enterprise_search_tool import enterprise_web_search_tool as enterprise_web_search
 from .example_tool import ExampleTool
 from .exit_loop_tool import exit_loop
 from .function_tool import FunctionTool
@@ -36,6 +37,7 @@ __all__ = [
     'APIHubToolset',
     'AuthToolArguments',
     'BaseTool',
+    'enterprise_web_search',
     'google_search',
     'url_context',
     'VertexAiSearchTool',

src/google/adk/tools/enterprise_search_tool.py

@@ -65,3 +65,6 @@ class EnterpriseWebSearchTool(BaseTool):
           'Enterprise web search tool is not supported for model'
           f' {llm_request.model}'
       )
+
+
+enterprise_web_search_tool = EnterpriseWebSearchTool()