Add k3s cluster expansion documentation and scripts

- Complete expansion guide for 2/4/6 node scenarios
- Quick join scripts for worker and master nodes
- Health check and diagnostic scripts
- Quick reference card for common operations

k3s/my-blog/Dockerfile

@@ -0,0 +1,8 @@
+# Custom WordPress image with Redis PHP extension
+FROM wordpress:latest
+
+# Install Redis PHP extension
+RUN pecl install redis && docker-php-ext-enable redis
+
+# Verify installation
+RUN php -m | grep redis