Document the new [MediaMetadata] amule.conf settings (media metadata extraction)

[got3nks]

amule-org/amule#280 (closes #140) added two new amule.conf settings that aren't yet on the config reference page:

📄 https://amule-org.github.io/docs/manual/configuration/config-files/amule-conf

Please add entries for the new [MediaMetadata] section:

Setting	Section	Type	Default	Description
Enabled	[MediaMetadata]	bool	0	Master switch for local media probing. When on, newly shared audio/video files are probed with ffprobe and the resulting duration / bitrate / codec are stamped as FT_MEDIA_{LENGTH,BITRATE,CODEC} tags in known.met, then advertised in ed2k search replies and Kad keyword publishes.
FFProbePath	[MediaMetadata]	string	(empty)	Path to the ffprobe executable. Empty means "not configured — no probing runs". A bare ffprobe value works when the binary is on the daemon's shell PATH; an absolute path is used verbatim.

A bit more detail worth capturing:

• The GUI surface is Preferences → Files → "Media metadata extraction", with a Detect button that auto-populates FFProbePath from the PATH plus a small set of well-known install locations (Homebrew, Chocolatey, Scoop, C:\ffmpeg\bin\ffprobe.exe, /snap/bin/ffprobe, etc.).
• Only audio and video extensions (ED2KFT_AUDIO / ED2KFT_VIDEO) are probed; other file types are skipped at the schedule gate.
• Probing runs on a low-priority worker thread (CThreadScheduler at ETP_Low) — never on the main thread. Already-probed files (whose FT_MEDIA_LENGTH tag persisted from a previous session) are skipped, so enabling the feature does not re-scan the entire share.
• Both settings are daemon-side only: amulegui hides the whole tile group when talking to a remote amuled, since the ffprobe path is a filesystem path on the daemon's host. Change them from the daemon-side GUI or edit amule.conf directly and restart.
• The feature ships disabled by default; users opt in.