feat: add devcontainer support

This should make it possible to run tests locally in a lighter way than pulling up a full VM.

.devcontainer/devcontainer.json

@@ -0,0 +1,8 @@
+{
+  "build": {
+    "dockerfile": "Dockerfile",
+    "context": ".."
+  },
+  "runArgs": ["--init"],
+  "mounts": [ "source=/var/run/docker.sock,target=/var/run/docker.sock,type=bind" ]
+}