Add devcontainer and gitpod

Also works in codespaces.

.devcontainer/Dockerfile

@@ -0,0 +1,5 @@
+ARG VARIANT=11-bullseye
+FROM mcr.microsoft.com/vscode/devcontainers/java:0-${VARIANT}
+
+ARG NODE_VERSION="none"
+RUN if [ "${NODE_VERSION}" != "none" ]; then su vscode -c "umask 0002 && . /usr/local/share/nvm/nvm.sh && nvm install ${NODE_VERSION} 2>&1"; fi

.devcontainer/devcontainer.json

@@ -0,0 +1,25 @@
+{
+	"name": "Petclinic",
+	"dockerFile": "Dockerfile",
+
+	"customizations": {
+		"vscode": {
+			"extensions": [
+				"vscjava.vscode-java-pack",
+				"redhat.vscode-xml"
+			]
+		}
+	},
+    "runArgs": [
+        "--cap-add=SYS_PTRACE", "--security-opt", "seccomp=unconfined",
+        "--mount", "type=bind,source=${env:HOME}/.m2,target=/home/vscode/.m2",
+        "--mount", "type=bind,source=${env:HOME}/.gradle,target=/home/vscode/.gradle"
+    ],
+
+    "initializeCommand": "mkdir -p ${env:HOME}/.m2 ${env:HOME}/.gradle",
+    "onCreateCommand": "sudo chown vscode:vscode /home/vscode/.m2 /home/vscode/.gradle",
+	"remoteUser": "vscode",
+	"features": {
+		"docker-in-docker": "latest"
+	}
+}