Pass to yt_dlp a chapter-specific output template

When a FFmpegSplitChapters postprocessor is used it is taken into account, in all other cases the default output template is used.

app/main.py

@@ -19,6 +19,7 @@ class Config:
         'STATE_DIR': '.',
         'URL_PREFIX': '',
         'OUTPUT_TEMPLATE': '%(title)s.%(ext)s',
+        'OUTPUT_TEMPLATE_CHAPTER': '%(title)s - %(section_number)s %(section_title)s.%(ext)s',
         'YTDL_OPTIONS': '{}',
     }