Serve "Cache-Control: no-cache" for non-bundled files. (#20489)

Most of the application is built into bundles with unique prefixes and
can be ignored, but these files should be checked each load.

nginx/conf.d/default.conf

@@ -6,11 +6,20 @@ server {
     root   /usr/share/nginx/html;
     index  index.html;
 
-    # Set no-cache for the index.html only so that browsers always check for a new copy of Element Web.
+    # Set no-cache for the version, config and index.html
+    # so that browsers always check for a new copy of Element Web.
+    # NB http://your-domain/ and http://your-domain/? are also covered by this
+
     location = /index.html {
         add_header Cache-Control "no-cache";
     }
-
+    location = /version {
+        add_header Cache-Control "no-cache";
+    }
+    # covers config.json and config.hostname.json requests as it is prefix.
+    location /config {
+        add_header Cache-Control "no-cache";
+    }
     # redirect server error pages to the static page /50x.html
     #
     error_page   500 502 503 504  /50x.html;