Move properties, parameters, events, and concepts around manual sections

The pages moved as follows:

zpool-features.{5 => 7}
spl{-module-parameters.5 => .4}
zfs{-module-parameters.5 => .4}
zfs-events.5 => into zpool-events.8
zfsconcepts.{8 => 7}
zfsprops.{8 => 7}
zpoolconcepts.{8 => 7}
zpoolprops.{8 => 7}

Reviewed-by: Richard Laager <rlaager@wiktel.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Co-authored-by: Daniel Ebdrup Jensen <debdrup@FreeBSD.org>
Closes #12149
Closes #12212