feat(infra/k8s): Rewrite cgit URLs by routing them through nginx

Configures nginx to rewrite all requests to cgit, except for those
retrieving static files, to `/depot/`.

In combination with the previous commits that apply patches to cgit
itself, this effectively means that the depot is rendered on the site
root.

This is pretty cool: It lets people do stuff like `git clone
https://git.tazj.in` and get the depot!

infra/kubernetes/nginx/nginx.conf

@@ -41,4 +41,19 @@ http {
             return 302 https://www.google.com/maps/d/viewer?mid=1pJIYY9cuEdt9DuMTbb4etBVq7hs;
         }
     }
+
+    server {
+        listen       80;
+        server_name  git.tazj.in;
+
+        # Static assets must always hit the root.
+        location ~ ^/(favicon\.ico|cgit\.(css|png))$ {
+           proxy_pass http://cgit;
+        }
+
+        # Everything else hits the depot directly.
+        location / {
+            proxy_pass http://cgit/cgit.cgi/depot/;
+        }
+    }
 }