feat: Add configurable real IP forwarding for bare-metal clusters

Implement a new nginx.forwardRealIP configuration flag to enable/disable
real client IP extraction from X-Forwarded-For headers on bare-metal clusters.

Changes:
- Added nginx.forwardRealIP.enabled flag (default: false) to values.yaml
- Added nginx.forwardRealIP.trustedProxies list for flexible proxy IP ranges
- Updated Nginx configmap to conditionally apply real IP extraction settings
- Updated FastCGI parameters to use real IP when enabled, direct connection IP otherwise
- Updated WordPress wp-config.php to conditionally extract real IPs from headers

Configuration:
- When enabled: Extracts real client IP from X-Forwarded-For header
- When disabled: Uses direct connection IP (default Nginx behavior)
- Supports custom proxy IP ranges for CloudFlare, AWS ALB, etc.

This allows Helmchart to work seamlessly on both:
1. Bare-metal clusters with iptables load balancing
2. Cloud-managed clusters with proper IP forwarding

Version bumped to 6.9.0-a (WordPress version with implementation suffix)

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

values.yaml

@@ -45,26 +45,20 @@ wordpress:
       # google.com, pub-0000000000000000, DIRECT, f08c47fec0942fa0
 
 nginx:
-  extraConfig: |
-    # リアルIPの取得設定
-    real_ip_header X-Forwarded-For;
-    real_ip_recursive on;
-    
-    # Kubernetesクラスタ内のIPレンジを信頼
-    set_real_ip_from 10.0.0.0/8;
-    set_real_ip_from 172.16.0.0/12;
-    set_real_ip_from 192.168.0.0/16;
-    
-    # CloudflareやAWS ALB等を使っている場合は追加
-    # set_real_ip_from 173.245.48.0/20;
-    # set_real_ip_from 103.21.244.0/22;
-    # ... (Cloudflareの他のIPレンジ)
+  # ベアメタルクラスター等でリアルIPを取得する設定
+  # ローカルIP（ベアメタル等）から訪問者のリアルIPを取得する場合に有効にします
+  forwardRealIP:
+    enabled: false
+    # 信頼できるプロキシのIPレンジを追加してください
+    trustedProxies:
+      - 10.0.0.0/8
+      - 172.16.0.0/12
+      - 192.168.0.0/16
+    # CloudflareやAWS ALB等を使っている場合は以下のIPレンジも追加してください
+    # - 173.245.48.0/20
+    # - 103.21.244.0/22
 
-  # FastCGIパラメータにリアルIPを渡す
-  fastcgiParams:
-    REMOTE_ADDR: $remote_addr
-    HTTP_X_REAL_IP: $realip_remote_addr
-    HTTP_X_FORWARDED_FOR: $proxy_add_x_forwarded_for
+  extraConfig: |
 
 # Service設定
 service: