Fix config and credential changes not being sent to Kubernetes charms

[Cynerva]

Partial fix for https://bugs.launchpad.net/bugs/1915557

Depends on juju-solutions/interface-azure-integration#8

When cloud configuration or credentials change, resend cloud data to units whose requests have already been processed.

There's a bit of nasty stuff in here to handle the variety of cases in which cloud credentials can change. From a high level, here's what you need to know:

1. If the charm config changes in any way (user runs juju config azure-integrator <foo>), then the charm's config-changed hook will run, with the config.changed flag set, and that will cause handle_requests to run and refresh requests.
2. If the charm is not configured with credentials directly, then it pulls credentials from Juju instead. When the user updates those credentials with a command like juju update-credential, Juju will not inform the charm that those credentials have changed. So we monitor for changes on the update-status hook instead, which ensures that the credentials will at least be updated eventually (typically within 5 minutes).
3. Given that the update-status hook only runs every 5 minutes, we provide an optional refresh-credentials action to force an immediate refresh of the credentials.

[addyess]

Sure thing here. This flows so beautifully.