www/yt-dlp: Make py-SecretStorage an optional port dependency

py-SecretStorage pulls a lot of dependencies for a small
optional feature in yt-dlp.

The upstream merged the PR that also makes SecretStorage optional:
https://github.com/yt-dlp/yt-dlp/pull/8585

PR:		275196
Submitted by:	Helge Oldach <freebsd@oldach.net> (initial version)