fix: use-case while in cluster, connecting to an external

[arbreezy]

Closes #604

📑 Description

There is a use case where people will run k8sgpt within a management cluster, as a pivot to other clusters where they can define explicitly the kubeconfig.
This small PR hopefully addresses that case by ensuring whenever kubeconfig is defined we will use it to create the k8s client even if k8sgpt is running in a cluster

✅ Checks

• My pull request adheres to the code style of this project
• My code requires changes to the documentation
• I have updated the documentation as required
• All the tests have passed

ℹ Additional Information