Add HLS (.m3u8) audio-only streaming file (#252)

Add an audio-only HTTP Live Streaming (HLS) .m3u8 file to test in the video_player_avfoundation plugin flutter/packages#7890

Created from the existing bee.mp4 video:

```
ffmpeg -i bee.mp4 -vn -c:a aac -b:a 128k audio_only.aac

ffmpeg -i audio_only.aac -c:a aac -b:a 128k -ar 44100 -start_number 0 -hls_time 10 -hls_list_size 0 -f hls bee_audio_only.m3u8
```

Related issues: [flutter/flutter#156589](flutter/flutter#156589)

Author: napoleon-na

assets/videos/hls/bee_audio_only.m3u8

@@ -0,0 +1,7 @@
+#EXTM3U
+#EXT-X-VERSION:3
+#EXT-X-TARGETDURATION:4
+#EXT-X-MEDIA-SEQUENCE:0
+#EXTINF:4.076956,
+bee_audio_only0.ts
+#EXT-X-ENDLIST