Currently horizon supports per-dashboard configurations in
/etc/openstack-dashboard/local_settings.d. Each dashboard plugin
provides a specific file to define its parameters, and any parameters
used in dashboard plugins have been removed from the base
local_settings(.py) in horizon repo.
To follow how each plugin is supposed to have its configurations
managed, this change introduces an independent file for heat-dashboard.
Support for the other dashboards like manila-ui, octavia-ui, and etc
will be added later.