Bump up Ansible supported versions to 7.x/8.x

This change bumps up the maximum supported version of Ansible to 8.x
(ansible-core 2.15.x) and minimum to 7.x (ansible-core 2.14.x).

Depends on:
https://github.com/stackhpc/ansible-role-systemd-networkd/pull/10

https://github.com/stackhpc/ansible-role-dell-powerconnect-switch/pull/13

https://github.com/stackhpc/ansible-role-mellanox-switch/pull/8

gateway_ip was being set to empty string. This was triggering neutron
""Invalid input for gateway_ip. Reason: '' is not a valid IP address."
Omitting by default.

Installing openstack.cloud collection.
Upgrade failed as Ansible in kayobe-venv was not upgraded.

Change-Id: Ia3550644e5fc3e83f792e46d42b4c35d5eec4705