fix: attempt to make linux builds faster (#911)

This work aims to make Linux builds faster to make https://github.com/ooni/probe/issues/2249 more convenient. Since those builds runs inside Docker, the problem to solve here is to save/restore the Go caches notwithstanding Docker. Because Docker runs as root, we need to modify the build a bit to run as a normal user. Otherwise, we will not be able to save the Go cache using actions/cache@v3. (Other approaches such as using `sudo` are possible but running the build as an unprivileged user actually looks cleaner, so I chose to do that.) While there, add a `.editorconfig`.

.vscode/settings.json

@@ -1,3 +1,8 @@
 {
-    "python.formatting.provider": "black"
-}
+    "python.formatting.provider": "black",
+    "gopls": {
+        "build.directoryFilters": [
+            "-GOCACHE"
+        ]
+    }
+}