package: move OpenBSM auditing into its own package

Move auditing runtime (auditd, etc.) into the new FreeBSD-audit package.
Also move the runtime OpenBSM manual pages from libbsm into auditd so
they get installed with the right package.

Add an UPDATING entry noting the new packages.

Reviewed by: imp, manu
Pull Request: https://github.com/freebsd/freebsd-src/pull/1197