Ensure stx-openstack is migrated to helmv3 on stx.8, before upgrading to stx.9.0

[Dan Voiculeasa]

Raising this to track possible work needed.
We must ensure stx-openstack is migrated to HelmV3 in stx.8.0.

Reasoning: migrate_helm_release.py needs to be removed since Armada and HelmV2 is removed in https://review.opendev.org/q/topic:remove-armada-helmv2 (stx.9.0). migrate_helm_release.py is removed in https://review.opendev.org/c/starlingx/config/+/865593.

Support needs to be implemented in stx-openstack if we don't already support this. A patchback to stx.8.0 is required in this case.
A doc change is required to enforce the migration on stx.8.0 side.