Add option to disable a pre upgrade check

[samuelallan72]

Sometimes there might be a minor issue on the cloud, one that won't affect upgrades. For example, I have a case where glance-simplestreams-sync has workload status blocked because it failed to sync images.

In these cases, COU will currently fail the pre-upgrade checks and refuse to continue the upgrade:

$ cou upgrade
...
Running cloud upgrade...
Verify that all OpenStack applications are in idle state ✖
2024-07-03 01:51:59 [ERROR] Unit in blocked: glance-simplestreams-sync/0
2024-07-03 01:51:59 [ERROR] See the known issues at https://canonical-charmed-openstack-upgrader.readthedocs-hosted.com/en/stable/reference/known-issues/

I'd like a way to ignore the check so I can continue the upgrade without being blocked.

It should be a fine grained ignore, to avoid over-ignoring issues. For example:

cou upgrade --ignore-check 'blocked.*glance-simplestreams-sync'

[gabrielcocenza]

I understand how frustrating this can be, but at the same time being able to ignore is a good way to shoot in the foot