Improve youtube loader (#3395)
Small improvements for the YouTube loader:
a) use the YouTube API permission scope instead of Google Drive
b) bugfix: allow transcript loading for single videos
c) an additional parameter "continue_on_failure" for cases when videos
in a playlist do not have transcription enabled.
d) support automated translation for all languages, if available.
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Co-authored-by: Johann-Peter Hartmann <johann-peter.hartmann@mayflower.de>
