Test: scale application to zero units

[BalabaDmitri]

Test cases

1. Deploy the primary cluster with 3 units , deploy the second cluster, continuously write ON, create test data, and check data.
2. Scale to 0 units, check shutdown all units.
3. Replace hostpath of the second cluster
4. Scale to 1 unit and check blocked status.
5. Down-scale the unit to 0 check shutdown all units.
6. Replace hostpath of the primary cluster
7. Scale to 1 unit, check the test data
8. Scale to 3 unit, check test data

Implementation

1. Charm blocked when use another cluster's storage.

[github-actions]

https://warthogs.atlassian.net/browse/DPE-4669