Include new notification options in sample config

Some new configuration options were added with the change to add
notifications to Keystone, but these new options weren't added
to the sample config file.

This change adds the new options to the sample configuration
file along with the descriptions from
keystone.openstack.common.notifier.api.

Also, if the Keystone server uses the RPC options from
keystone/openstack/common/rpc/__init__.py if using the RPC
notification driver, so these options are also added to the
sample config file.

Having these options in the config file will make it easier for
administrators to update the configuration values.

DocImpact
Change-Id: I85f2450a6fb68d51453adbb5413ad48fe00ca17e
Merge "Include new notification options in sample config"