XWiki: increase installer execution timeout and add retries

The task 'XWIKI | Execute installer page' now uses:
- timeout: 300 (allow up to 5 min per request)
- retries: 20
- delay: 15
- until: condition

This prevents early failures during the first Distribution Wizard bootstrap when hundreds of extensions are still being installed.

Context: https://chatgpt.com/share/68ca0f18-2124-800f-a70d-df1811966107

roles/web-app-xwiki/templates/env.j2

@@ -4,3 +4,4 @@ DB_HOST="{{ database_host }}"
 DB_PORT="{{ database_port }}"
 DB_DATABASE="{{ database_name }}"
 DB_TYPE="{{ 'mariadb' if database_type == 'mariadb' else 'postgresql' }}"
+XWIKI_SUPERADMIN_PASSWORD="{{ XWIKI_SUPERADMIN_PASSWORD }}"