A train template is added which pulls in sectional
placement config from charm-layer-openstack.
This requires adding identity-credentials as a required
interface for train and above.
This patch also updates the smoke test to run train.
Closes-Bug: 1850691
Depends-On: https://review.opendev.org/#/c/692426/
Change-Id: Ib3937915c5195b5e031d5056959932849012fc23
Signed-off-by: Sahid Orentino Ferdjaoui <sahid.ferdjaoui@canonical.com>