Upgrade multimedia chapter

• Rework the chapter:

• Upgrade sound section, tell the user that FreeBSD recognizes the sound card and there is no need to load any modules. Only in the very rare case that the sound card is not recognized.

• Add table with sound mixers
• Add info about how to automatically switching to headphones
• Add table with audio players
• Add table with video players
• Add a new section about conferencing and meetings, inspired by [1]
• Rework the image scanners section

The webcam and scanner has been tested in a clean installation in
FreeBSD 13.1 with the laptop "HP Notebook - 15-bw048ns" and
the scanner "HP Deskjet 1050 J410"

[1] https://vermaden.wordpress.com/2021/05/26/freebsd-desktop-part-26-configuration-conferencing-and-meetings/

Reviewed by: arrowd, fernape, emaste
PR: 262068, 266022
Differential Revision: https://reviews.freebsd.org/D38798