YouTube transcription variable

[dpigera]

Summary

This PR addresses introducing a transcript variable that pulls down transcripts via the YouTube template
Issue link: #274

Changes Introduced:

• Added a getTranscript() method to utils/extractors/youtube.ts which pulls the transcript lines from ytd-transcript-segment-renderer and adds the timestamp, timestamp_link, and caption text
• Introduced a transcript variable
• Also introduced a method to auto-click the 'Show Transcript' button. Unsure if this is a good user experience. Open to refactoring according to product needs

Testing Done

• Compiled and ran web clipper in Safari Extensions developer mode
• Opened YouTube video
• Opened Settings, Templates, Added JSON from youtube.json template file
• Added {{transcript}} variable
• Clicked 'Show Transcript' button, and ran clipper
• Transcript included. Example pull:

![How to Reclaim Your Life From Work | Simone Stolzoff | TED](https://www.youtube.com/watch?v=cfKFbh8LPvU)

[0:04](https://youtube.com/watch?v=cfKFbh8LPvU&t=4s) I once met this Chilean guy at a hostel.
[0:08](https://youtube.com/watch?v=cfKFbh8LPvU&t=8s) "So what do you do?" I asked him.
[0:11](https://youtube.com/watch?v=cfKFbh8LPvU&t=11s) "You mean for work?"

Screenshot