refactor: move proxy to monorepo

backend/proxy/fixtures/metrics.template

@@ -0,0 +1,14 @@
+map $status $omitOKs {
+  default 1;
+  ~^[2][0][0] 0;
+}
+
+server {
+    listen 8080;
+    error_log stderr;
+    access_log /dev/stdout {{{ logFormat }}} if=$omitOKs;
+    location /metrics {
+        vhost_traffic_status_display;
+        vhost_traffic_status_display_format prometheus;
+    }
+}