Provide new directory environment properties that can be used to indicate
whether the server should maintain a configuration archvie, and if so the
maximum number of archived configurations that it should keep.  By default, the
archive will be enabled and will be configured to keep an unlimited number of
previous configurations.

This needs to be controlled via a directory environment property rather than a
configuration option, since first part of configuration archive processing
happens before the server has read and processed the configuration.  The
DirectoryEnvironmentConfig class provides methods for interacting with these
settings.