Add devcontainer for ubuntu

.devcontainer/Dockerfile

@@ -0,0 +1,6 @@
+ARG VARIANT="jammy"
+FROM ghcr.io/sagemath/sage/sage-docker-ubuntu-${VARIANT}-standard-with-system-packages:dev
+
+# Install additional packages needed for devcontainer support in VS code
+RUN apt-get update && export DEBIAN_FRONTEND=noninteractive \
+    && apt-get -y install --no-install-recommends gpgconf openssh-client

.devcontainer/devcontainer.json

@@ -0,0 +1,11 @@
+// For format details, see https://aka.ms/devcontainer.json.
+{
+	"name": "Ubuntu",
+	"build": {
+		"dockerfile": "Dockerfile",
+		// Update 'VARIANT' to pick an Ubuntu version: hirsute, focal, bionic, xenial, trusty, etc.
+		"args": { "VARIANT": "jammy" }
+	},
+	// Run commands after the container is started.
+	"postStartCommand": "configure && make build"
+}

.vscode/settings.json

@@ -19,4 +19,7 @@
         "src"
     ],
     "python.testing.unittestEnabled": false,
+    "cSpell.words": [
+        "sagemath"
+    ],
 }