Add remote cluster connection capabilities

Enhance TroubleKuber to better support remote Kubernetes clusters:

Features to implement

• Add support for multiple kubeconfig files
• Create context switching capabilities
• Implement cluster connection validation
• Add secure credential handling
• Support for storing and managing multiple cluster connections
• Add connection troubleshooting capabilities

Implementation details

• Create lib/resources/cluster.sh module
• Add kubeconfig management utilities
• Implement context switching in the UI
• Add connection validation before operations
• Create connection troubleshooting functions
• Add documentation for connecting to different cluster types