adds devcontainer/codespaces support (#6250)

deploy/codespaces/install.sh

@@ -0,0 +1,9 @@
+#!/bin/bash
+set -xeuf -o pipefail
+
+# exit this file if we are not in Codespaces
+if [ -z "${CODESPACES}" ]; then
+  exit 0
+fi
+
+echo "echo \"🚀 Welcome to Cal.com! Try typing 'yarn dx' to get a quick dev envionment.\"" >> ~/.bashrc