Add init script to load keys

Add new init scripts which allow automatic loading of keys if
keylocation property is set to a URI.

Reviewed-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Benedikt Neuffer <ogelpre@itfriend.de>
Closes #11659
Closes #11662