Add devcontainer config

.devcontainer/Dockerfile

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+# [Choice] Ruby version (use -bullseye variants on local arm64/Apple Silicon): 3, 3.0, 2, 2.7, 2.6, 3-bullseye, 3.0-bullseye, 2-bullseye, 2.7-bullseye, 2.6-bullseye, 3-buster, 3.0-buster, 2-buster, 2.7-buster, 2.6-buster
+ARG VARIANT=2-bullseye
+FROM mcr.microsoft.com/vscode/devcontainers/ruby:0-${VARIANT}
+
+# Install Rails
+RUN gem install rails webdrivers
+
+# Default value to allow debug server to serve content over GitHub Codespace's port forwarding service
+# The value is a comma-separated list of allowed domains
+ENV RAILS_DEVELOPMENT_HOSTS=".githubpreview.dev"
+
+# [Choice] Node.js version: lts/*, 16, 14, 12, 10
+ARG NODE_VERSION="lts/*"
+RUN su vscode -c "source /usr/local/share/nvm/nvm.sh && nvm install ${NODE_VERSION} 2>&1"

.devcontainer/create-db-user.sql

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+CREATE USER vscode CREATEDB;
+CREATE DATABASE vscode WITH OWNER vscode;

.devcontainer/devcontainer.json

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+// For format details, see https://aka.ms/devcontainer.json. For config options, see the README at:
+// https://github.com/microsoft/vscode-dev-containers/tree/v0.208.0/containers/ruby-rails-postgres
+// Update the VARIANT arg in docker-compose.yml to pick a Ruby version
+{
+	"name": "Ruby on Rails & Postgres",
+	"dockerComposeFile": "docker-compose.yml",
+	"service": "app",
+	"workspaceFolder": "/workspace",
+
+	// Set *default* container specific settings.json values on container create.
+	"settings": {
+		"sqltools.connections": [
+			{
+				"name": "Rails Development Database",
+				"driver": "PostgreSQL",
+				"previewLimit": 50,
+				"server": "localhost",
+				"port": 5432,
+
+				// update this to match config/database.yml
+				"database": "app_development",
+				"username": "vscode"
+			},
+			{
+				"name": "Rails Test Database",
+				"driver": "PostgreSQL",
+				"previewLimit": 50,
+				"server": "localhost",
+				"port": 5432,
+
+				// update this to match config/database.yml
+				"database": "app_test",
+				"username": "vscode"
+			}
+		]
+	},
+
+	// Add the IDs of extensions you want installed when the container is created.
+	"extensions": [
+		"rebornix.Ruby",
+		"mtxr.sqltools",
+		"mtxr.sqltools-driver-pg"
+	],
+
+	// Use 'forwardPorts' to make a list of ports inside the container available locally.
+	// "forwardPorts": [3000, 5432],
+
+	// Use 'postCreateCommand' to run commands after the container is created.
+	"postCreateCommand": "script/create-sample-app",
+
+	// Comment out connect as root instead. More info: https://aka.ms/vscode-remote/containers/non-root.
+	"remoteUser": "vscode"
+}

.devcontainer/docker-compose.yml

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+version: '3'
+
+services:
+  app:
+    build:
+      context: ..
+      dockerfile: .devcontainer/Dockerfile
+      args:
+        # Update 'VARIANT' to pick a version of Ruby: 3, 3.0, 2, 2.7, 2.6
+        # Append -bullseye or -buster to pin to an OS version.
+        # Use -bullseye variants on local arm64/Apple Silicon.
+        VARIANT: "3"
+        # Optional Node.js version to install
+        NODE_VERSION: "lts/*"
+
+    volumes:
+      - ..:/workspace:cached
+
+    # Overrides default command so things don't shut down after the process ends.
+    command: sleep infinity
+
+    # Runs app on the same network as the database container, allows "forwardPorts" in devcontainer.json function.
+    network_mode: service:db
+    # Uncomment the next line to use a non-root user for all processes.
+    # user: vscode
+
+    # Use "forwardPorts" in **devcontainer.json** to forward an app port locally.
+    # (Adding the "ports" property to this file will not forward from a Codespace.)
+
+  db:
+    image: postgres:latest
+    restart: unless-stopped
+    volumes:
+      - postgres-data:/var/lib/postgresql/data
+      - ./create-db-user.sql:/docker-entrypoint-initdb.d/create-db-user.sql
+    environment:
+      POSTGRES_USER: postgres
+      POSTGRES_DB: postgres
+      POSTGRES_PASSWORD: postgres
+    # Add "forwardPorts": ["5432"] to **devcontainer.json** to forward PostgreSQL locally.
+    # (Adding the "ports" property to this file will not forward from a Codespace.)
+
+volumes:
+  postgres-data: null