packages: Rename unbound to local-unbound

This more accurately reflects its purpose, and its contents, since
everything in the package is prefixed with "local-".

While here, add a message on upgrade about regenerating the config.

MFC after:	3 seconds
Requested by:	des
Reviewed by:	des
Sponsored by:	https://www.patreon.com/bsdivy
Differential Revision:	https://reviews.freebsd.org/D53056

UPDATING

@@ -27,6 +27,14 @@ NOTE TO PEOPLE WHO THINK THAT FreeBSD 16.x IS SLOW:
 	world, or to merely disable the most expensive debugging functionality
 	at runtime, run "ln -s 'abort:false,junk:false' /etc/malloc.conf".)
 
+20251015:
+	The "FreeBSD-unbound" package is renamed to "FreeBSD-local-unbound".
+	If you have set-optional or set-base installed, the new package will
+	be installed automatically, otherwise you should manually install the
+	new package and remove the old one.
+
+	This change only affects pkgbase users.
+
 20251012:
 	Blacklist has been renamed upstream to Blocklist.  If you have it
 	configured, rename all configuration files, firewall anchors or