[EPIC] Refactor Config

[manusa]

Description

The issue redhat-developer/intellij-kubernetes#779 required an involved fix that @adietish reported in #6240 and implemented in #6295 🙌.

The fix, however, has unveiled the amount of convoluted and coupled code present in the Config loading logic, Config refreshing logic, and Config update persisting logic.

We need to refactor and decouple all of this logic to guarantee an easy maintenance and allow to add newer functionality for the Kubernetes Client Config.
This is a critical class that affects the rest of the code-base.
Having clear, concise, and maintainable Config procedures is a must for the future of the project.

Tasks

• Remove mocked config from OpenShiftOAuthInterceptorTest #6517
• Make public static constants in OpenIDConnectionUtils private #6519
• Remove deprecated Config.impersonateGroup #6521
• Provide a Config.fromKubeconfig(Path|File) method and deprecate the current ones #6525
• Remove Config deprecated constructors #6528
• Create specific behavioral tests for Config refresh #6535
• Remove Config.setFile setter, should rely on builder #6542
• Remove Config.setAutoConfigure internal setter #6544
• Config.refresh shouldn't use deprecated fromKubeconfig method #6547
• Config.getKubeconfigFilename should return a collection of files #6549
• KubeConfigUtils.merge should support multiple files #6551
• Config.getFile can be inferred from Config.currentContext #6554
• Config.autoConfigure should support multiple files #6556
• Config supports reading multiple kubeconfig files with scattered information #6558
• merge multiple files listed in KUBECONFIG environment var #6240
• Remove unused impersonate-related fields from Config #6565

References

• Cannot get my clusters to appear redhat-developer/intellij-kubernetes#779