docs(contribution): update templates with modern patterns (#10227)

Based on analysis of latest 30 scripts (koel, wallabag, invoiceninja, etc.)

Templates updated to reflect current best practices:

ct/AppName.sh:
- Use check_for_gh_release + fetch_and_deploy_gh_release pattern
- CLEAN_INSTALL=1 for updates
- Proper backup/restore workflow
- Simplified configuration comments

install/AppName-install.sh:
- fetch_and_deploy_gh_release as primary download method (no separate RELEASE variable)
- Real-world examples from Node.js, Python, PHP apps
- import_local_ip called early
- Setup runtimes/databases before app installation
- cleanup_lxc at the end

HELPER_FUNCTIONS.md:
- fetch_and_deploy_gh_release as preferred method (documented first)
- CLEAN_INSTALL=1 environment variable documented
- prebuild type with asset_pattern documented
- Clarified when to use get_latest_github_release vs fetch_and_deploy

Closes #10194

docs/contribution/templates_json/AppName.json

@@ -1,34 +1,34 @@
 {
-    "name": "AppName",
-    "slug": "appname",
-    "categories": [
-        0
-    ],
-    "date_created": "DATE CREATED",
-    "type": "ct",
-    "updateable": true,
-    "privileged": false,
-    "interface_port": DEFAULT-PORT,
-    "documentation": null,
-    "website": "LINK TO WEBSITE",
-    "logo": "LINK TO LOGO",
-    "description": "Description of the app",
-    "install_methods": [
-        {
-            "type": "default",
-            "script": "ct/AppName.sh",
-            "resources": {
-                "cpu": 2,
-                "ram": 2048,
-                "hdd": 4,
-                "os": "debian",
-                "version": "12"
-            }
-        }
-    ],
-    "default_credentials": {
-        "username": null,
-        "password": null
-    },
-    "notes": []
-}
+  "name": "AppName",
+  "slug": "appname",
+  "categories": [
+    0
+  ],
+  "date_created": "DATE CREATED",
+  "type": "ct",
+  "updateable": true,
+  "privileged": false,
+  "interface_port": "DEFAULT-PORT",
+  "documentation": null,
+  "website": "LINK TO WEBSITE",
+  "logo": "LINK TO LOGO",
+  "description": "Description of the app",
+  "install_methods": [
+    {
+      "type": "default",
+      "script": "ct/AppName.sh",
+      "resources": {
+        "cpu": 2,
+        "ram": 2048,
+        "hdd": 4,
+        "os": "debian",
+        "version": "12"
+      }
+    }
+  ],
+  "default_credentials": {
+    "username": null,
+    "password": null
+  },
+  "notes": []
+}