feat: Add BigQuery analyze_contribution tool

This change introduces a new `analyze_contribution` function in `query_tool.py` which uses BigQuery ML's `CREATE MODEL` with `CONTRIBUTION_ANALYSIS` type and `ML.GET_INSIGHTS` to analyze the contribution of different dimensions to a given metric. The new function is also added to the `bigquery_toolset`.

PiperOrigin-RevId: 815849281

tests/unittests/tools/bigquery/test_bigquery_toolset.py

@@ -41,7 +41,7 @@ async def test_bigquery_toolset_tools_default():
   tools = await toolset.get_tools()
   assert tools is not None
 
-  assert len(tools) == 7
+  assert len(tools) == 8
   assert all([isinstance(tool, GoogleTool) for tool in tools])
 
   expected_tool_names = set([
@@ -52,6 +52,7 @@ async def test_bigquery_toolset_tools_default():
       "execute_sql",
       "ask_data_insights",
       "forecast",
+      "analyze_contribution",
   ])
   actual_tool_names = set([tool.name for tool in tools])
   assert actual_tool_names == expected_tool_names