Application explorer is broken if `KUBECONFIG` env var is set

[datho7561]

To reproduce:

1. set export KUBECONFIG='~/folder/config.yaml' in ~/.bashrc or similar
2. create the file referenced in the previous step, and add some sample data in it (eg. one of the kubeconfigs from https://kubernetes.io/docs/tasks/access-application-cluster/configure-access-multiple-clusters)
3. log in to a cluster, such as crc or Sandbox (this will create new entries in your new ~/folder/config.yaml for crc or sandbox)
4. start the extension
5. navigate to the openshift sidebar

expected: crc/sandbox is shown in the application explorer (the top item in the sidebar)

actual: there are three buttons: "Login", "Select Kubernetes Context", "Add OpenShift Cluster", and they are disabled

[datho7561]

I have a PR started for this. The main blocker I ran into is that you can configure multiple KUBECONFIG files: https://kubernetes.io/docs/tasks/access-application-cluster/configure-access-multiple-clusters/#linux-1

[datho7561]

the library we are using to load the kube config doesn't handle multiple kube config well