docs/ci: Document setting up the http cache for traces.

Reviewed-by: Daniel Stone <daniel@fooishbar.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8727>

docs/ci/fdo-cache

@@ -0,0 +1,44 @@
+proxy_cache_path /var/cache/nginx/ levels=1:2 keys_zone=my_cache:10m max_size=24g inactive=48h use_temp_path=off;
+
+server {
+	listen 10.42.0.1:8888 default_server;
+	listen 127.0.0.1:8888 default_server;
+	listen [::]:8888 default_server;
+	resolver 8.8.8.8;
+
+	root /var/www/html;
+
+	# Add index.php to the list if you are using PHP
+	index index.html index.htm index.nginx-debian.html;
+
+	server_name _;
+
+        add_header X-GG-Cache-Status $upstream_cache_status;
+        proxy_cache my_cache;
+
+        location /cache_gitlab_artifacts {
+                internal;
+                # Gitlabs http server puts everything as no-cache even though
+                # the artifacts URLS don't change. So enforce a long validity
+                # time and ignore the headers that defeat caching
+                proxy_cache_valid 200 48h;
+                proxy_ignore_headers Cache-Control Set-Cookie;
+                include snippets/uri-caching.conf;
+        }
+
+        location /cache {
+                # special case gitlab artifacts
+                if ($arg_uri ~*  /.*gitlab.*artifacts(\/|%2F)raw/ ) {
+                        rewrite ^ /cache_gitlab_artifacts;
+                }
+                # Set a really low validity together with cache revalidation; Our goal
+                # for caching isn't to lower the number of http requests but to
+                # lower the amount of data transfer. Also for some test
+                # scenarios (typical manual tests) the file at a given url
+                # might get modified so avoid confusion by ensuring
+                # revalidations happens often.
+                proxy_cache_valid 200 10s;
+                proxy_cache_revalidate on;
+                include snippets/uri-caching.conf;
+        }
+}