[DBaaS] Create DB cluster option on UI is enabled while EKS/Minikube cluster is in provisioning state

User impact:

User is able to see and use an enabled option to create a DB cluster while the kubernetes cluster is still in provisioning state.

Steps to reproduce:

1. To reproduce a K8s cluster that has operators installed but its state is still "Provisioning" (This is how it did for me, there might other scenarios to reproduce this)
   1. Create an EKS cluster
   2. Register it to a PMM instance
   3. Unregister it from that PMM instance
   4. Register the same EKS cluster to another PMM instance after two or three days
2. Create a DB cluster on that EKS cluster:
   1. Register a fresh minikube or EKS cluster that gets resgistered successfully with operators installed and state being active.
   2. Click "Create DB cluster" option against that active cluster.
   3. In the "Create DB Cluster" window, select that EKS cluster (one that is in provisioning state) from the drop-down menu "Kubernetes Cluster"
   4. Create a DB cluster by filling in other required options

Actual result:

On "Create DB Cluster" window, it lets you select any kubernetes cluster even if the cluster is in provisioning state.

Expected result:

If the kubernetes cluster is in provisioning state, it should not be visible anywhere for DB cluster creation or any other relatable/similar option.