Get Douyin relation word analysis

Returns Douyin relation word analysis for a keyword, including search and content relation words. Send keyword, end_date (End date (must be Sunday) YYYYMMDD), start_date (Start date (Monday) YYYYMMDD); optional app_name. Returns search relation words, content relation words, relation word graph data. end_date: End date (must be a Sunday), format YYYYMMDD. The end_date must be a Sunday, e.g. start_date=20260330, end_date=20260405 (Sunday).