feat: Add custom User-Agent header to RestApiTool requests

src/google/adk/tools/openapi_tool/openapi_spec_parser/rest_api_tool.py

@@ -245,6 +245,7 @@ def _prepare_request_params(
     Example:
         self._prepare_request_params({"input_id": "test-id"})
     """
+
     method = self.endpoint.method.lower()
     if not method:
       raise ValueError("Operation method not found.")
@@ -254,6 +255,12 @@ def _prepare_request_params(
     header_params: Dict[str, Any] = {}
     cookie_params: Dict[str, Any] = {}
 
+    from ....version import __version__ as adk_version
+
+    # Set the custom User-Agent header
+    user_agent = f"google-adk/{adk_version} (tool: {self.name})"
+    header_params["User-Agent"] = user_agent
+
     params_map: Dict[str, ApiParameter] = {p.py_name: p for p in parameters}
 
     # Fill in path, query, header and cookie parameters to the request