ci: add devcontainer configuration (cloudnative-pg#2418)

The devcontainer configuration allows any user to instantly configure an environment
capable of running all the tests (including E2E) and works well with [devpod](http://devpod.sh)

Signed-off-by: Marco Nenciarini <marco.nenciarini@enterprisedb.com>
Signed-off-by: Leonardo Cecchi <leonardo.cecchi@enterprisedb.com>
Co-authored-by: Leonardo Cecchi <leonardo.cecchi@enterprisedb.com>

Author: mnencia

.devcontainer/devcontainer.json

@@ -0,0 +1,25 @@
+{
+  "image": "mcr.microsoft.com/devcontainers/go:1",
+  "features": {
+    "ghcr.io/devcontainers/features/docker-in-docker:2": {},
+    "ghcr.io/rio/features/k3d:1": {},
+    "ghcr.io/mpriscella/features/kind:1": {},
+    "ghcr.io/rjfmachado/devcontainer-features/cloud-native:1": {
+      "kubectl": "latest",
+      "helm": "latest",
+      "kubelogin": "none",
+      "azwi": "none",
+      "flux": "none",
+      "cilium": "none"
+    },
+    "ghcr.io/guiyomh/features/golangci-lint:0": {},
+    "ghcr.io/devcontainers-contrib/features/kubectx-kubens:1": {},
+    "ghcr.io/dhoeric/features/stern:1": {}
+  },
+
+  // Needed by kind and k3s to enable kube-proxy's ipvs mode
+  "mounts":["type=bind,source=/lib/modules,target=/lib/modules"],
+
+  // Enable kubectl short alias with completion
+  "postCreateCommand": "echo 'alias k=kubectl; complete -F __start_kubectl k' >> ~/.bash_aliases"
+}