chore(search): add Tavily key config placeholders

Signed-off-by: Asklv <boironic@gmail.com>

main/tools/tool_web_search.h

@@ -22,3 +22,8 @@ esp_err_t tool_web_search_execute(const char *input_json, char *output, size_t o
  * Save Brave Search API key to NVS.
  */
 esp_err_t tool_web_search_set_key(const char *api_key);
+
+/**
+ * Save Tavily API key to NVS.
+ */
+esp_err_t tool_web_search_set_tavily_key(const char *api_key);