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/web-app-openproject/tasks/main.yml

@@ -2,6 +2,8 @@
 - name: "load docker, db and proxy for {{ application_id }}"
   include_role:
     name: sys-stk-full-stateful
+  vars:
+    client_max_body_size: "30m"
 
 - name: "Create {{ OPENPROJECT_PLUGINS_FOLDER }}"
   file: