Respect the $KUBECONFIG env as top precedence

[Dentrax]

Checklist:

• I've searched for similar issues and couldn't find anything matching
• I've discussed this feature in the #k8sgpt slack channel

Is this feature request related to a problem?

• Yes
• No

On first try, I couldn't able to run k8sgpt:

$ k8sgpt analyze

Error initialising kubernetes client: invalid configuration: no configuration has been provided, try setting KUBERNETES_MASTER environment variable
Error: invalid configuration: no configuration has been provided, try setting KUBERNETES_MASTER environment variable

Even $KUBECONFIG is set and context is correct:

$ echo $KUBECONFIG

/Users/furkan.turkal/.kube/my-foo-cluster-kubeconfig

This means that k8sgpt is inconsistent with how kubectl handle this.

Current behavior is k8sgpt does not respect $KUBECONFIG env. You should manually copy the path of kubeconfig and pass --kubeconfig flag every time when you switch the context, which significantly decrease overall UX.

export KUBECONFIG=/path/to/your/kubeconfig1
k8sgpt analyze --kubeconfig /path/to/your/kubeconfig1 -e

export KUBECONFIG=/path/to/your/kubeconfig2
k8sgpt analyze --kubeconfig /path/to/your/kubeconfig2 -e

export KUBECONFIG=/path/to/your/kubeconfig3
k8sgpt analyze --kubeconfig /path/to/your/kubeconfig3 -e

Expected behavior:

export KUBECONFIG=/path/to/your/kubeconfig1
k8sgpt analyze -e

export KUBECONFIG=/path/to/your/kubeconfig2
k8sgpt analyze -e

export KUBECONFIG=/path/to/your/kubeconfig3
k8sgpt analyze -e

Describe the solution you'd like

Respect $KUBECONFIG env (if set) and it should be first precedence. (like how kubectl did)

Benefits for the project and its users

Consistency and better UX.

Potential drawbacks

It would be a backward-incompatible behavior.

Additional context

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