Revert "Simplify caching setup" (openmrs#880)

Author: vasharma05

frontend/nginx.conf

@@ -26,15 +26,15 @@ http {
     }
 
     # never cache the importmap, routes, or service-worker
-    location /service-worker.js {
+    location ~* (((importmap|routes\.registry)\.json)|service-worker\.js)$ {
       expires -1d;
       try_files $uri =404;
     }
 
     # handle anything with a "." that's not an HTML
     # assume it's a static file
     location ~* \.(?!html?)[^.]+$ {
-      add_header 'Cache-Control' 'no-cache, must-revalidate'
+      expires 6M;
       try_files $uri =404;
     }