Suggest --list-subs when no matching subtitle format found (Resolve #9760)

[wenbang24]

IMPORTANT: PRs without the template will be CLOSED

Description of your pull request and other information

Added "add the --list-subs flag to see a list of available subtitle formats" to YoutubeDL.py.

also its my first issue :)

Fixes #9760

Template

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[bashonly]

LGTM. In the future, please do not resolve review comments unless you are directly applying the suggested change(s)

[wenbang24]

so what do I do now?

[seproDev]

Nothing to do from your side. At some point a maintainer will merge this.