add SSL support in Openstack Heat

Hi,
I tried to generate a bundle with:

./generate-bundle.sh -s focal -r ussuri --heat-ha --ssl -n testssl

but the "ssl_ca", "ssl_cert" and "ssl_key" variables in the Heat charm are no used. It seems there is no support for SSL in Heat.

It would be helpful to add this feature.

Thank you.
Regards,
Marco