Uninstall should handle db2u

[durera]

Feature and motivation

When uninstalling a MAS instance:

• Look for, and offer to delete, any db2ucluster instances associated to the instance (which can be determined by their name)
• Also offer to delete the Db2u operator and namespace if there are no other db2ucluster instances in the db2u namespace

Usage example

When uninstalling a MAS instance the user may want to remove Db2uClusters associated with the instance.