(#5408) Attributes can be both audited and managed

This patch makes it possible to both audit and manage an attribute.
It introduces a new field on Event objects "historical_value", which is
the value from state.yaml. The value from the RAL is written to
state.yaml, and then the RAL is updated with the desired value.

Paired-With: Nick Lewis <nick@puppetlabs.com>
Paired-With: Matt Robinson <matt@puppetlabs.com>