Context-Specific Custom Views

[uozalp]

Add support for context-specific custom views in k9s, allowing users to define different column layouts for the same resource type across different Kubernetes clusters/contexts.

Motivation
When working with multiple Kubernetes clusters (production, staging, development, homelab etc), users might need different column layouts for the same resources:

Currently, k9s custom views are global across all contexts, forcing users to choose a single layout that may not be optimal for different environments.

Proposed Solution
Extend the existing custom views syntax to support context-specific patterns using the @context: suffix, similar to the existing @namespace pattern.

views:
  # Context-specific view for production
  v1/pods@context:production:
    columns:
      - NAMESPACE
      - NAME
      - STATUS
      - READY
      - NODE
      - RESTARTS

  # Context-specific view for development
  v1/pods@context:development:
    columns:
      - NAME
      - READY
      - RESTARTS
      - AGE
      - IP

  # Combined: namespace + context (most specific)
  v1/pods@kube-system@context:production:
    columns:
      - NAME
      - NODE
      - STATUS
      - AGE

  # Generic fallback for all contexts
  v1/pods:
    columns:
      - NAME
      - STATUS
      - AGE

Alternativ, but with the current design, YAML specification doesn't allow duplicate keys. Having multiple v1/pods: entries causes a parsing error: yaml: unmarshal errors: mapping key "v1/pods" already defined.

  v1/pods
    context: development
    columns:
      - NAME
      - READY
      - RESTARTS
      - AGE
      - IP

@derailed I have a PR ready, but need some inputs