[FR] File Embed Preview

[xbais]

When a file like a PDF file is embedded, the app should atleast provide a preview of the file:

1. PDF --> Image preview of first page of PDF document
2. Audio --> Audios can be easily embedded and played from within the application, the preview can show a waveform of the audio
3. Video --> Video preview can be taken from a random frame from within the video, or from the frame at 1/3 time of the video
4. TXT files (including UTF-8 formatted files) --> Preview can include the entire document added in a suitable code block.