Add support for RPKI Signed Prefix Lists

Add support for RPKI Signed Prefix Lists

Signed Prefix List are a CMS protected content type for use with the
RPKI to carry the complete list of prefixes which an Autonomous System
may originate to all or any of its routing peers. The validation of a
Signed Prefix List confirms that the holder of the listed ASN produced
the object, and that this list is a current, accurate and complete
description of address prefixes that may be announced into the routing
system originated by this AS.

https://datatracker.ietf.org/doc/html/draft-ietf-sidrops-rpki-prefixlist

with and OK claudio@ tb@