feat(proxy): add configurable client_max_body_size for HTML and upload locations

This commit introduces a unified mechanism to configure client_max_body_size
for both HTML and upload locations in the sys-svc-proxy role. The directive
is now injected early in html.conf.j2 and moved to a dedicated block in
upload.conf.j2 to ensure consistent behavior for large file uploads such as
OpenProject attachments.

Additionally:
- Added client_max_body_size variable override from web-app-openproject (set to 30m).
- Reordered header includes to avoid duplicate injection.
- Improved comments and structure for better clarity.

Reference: https://chatgpt.com/share/691d873e-9b50-800f-ae70-baf8bf1e5454

roles/sys-svc-proxy/templates/location/upload.conf.j2

@@ -1,13 +1,17 @@
 location {{ location_upload }} {
+    
+    # Proxyconfiguration for Upload
     proxy_pass              http://127.0.0.1:{{ http_port }};
     proxy_set_header        Host              $host;
     proxy_set_header        X-Real-IP         $remote_addr;
     proxy_set_header        X-Forwarded-For   $proxy_add_x_forwarded_for;
     proxy_set_header        X-Forwarded-Proto $scheme;
-    client_max_body_size    {{ client_max_body_size }};
     proxy_buffering         off;
     proxy_request_buffering off;
     proxy_read_timeout      120s;
     proxy_connect_timeout   120s;
     proxy_send_timeout      120s;
+
+    # Client Limits for Upload
+    client_max_body_size    {{ client_max_body_size }};
 }