DBaaS: Creating DB cluster with same name

User impact: 
User can now create multiple DB clusters with same name. If the cluster parameters are identical, nothing happens. If the parameters are different, the existing DB cluster is updated

STR:
Go to DBaaS page
Create a DB cluster
Create another DB cluster with same name

Actual result:

Expected result:
We probably should not let users create DB clusters with same name but show error as we do with same Kubernetes Clusters

Suggested implementation:

• Check in dbaas-controller that there is no db cluster with the same name before creating db cluster.
• Probably the best place to place check is
  • https://github.com/percona-platform/dbaas-controller/blob/main/service/k8sclient/k8client.go#L282
  • https://github.com/percona-platform/dbaas-controller/blob/main/service/k8sclient/k8client.go#L596
• Return error if db cluster is exists