Add support for CodeSpaces

.devcontainer/Dockerfile

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+ARG VARIANT=latest
+FROM elixir:${VARIANT}
+
+RUN apt-get update && \
+    apt-get install -y postgresql-client && \
+    apt-get install -y inotify-tools && \
+    apt-get install -y nodejs && \
+    apt-get install -y git && \
+    curl -L https://npmjs.org/install.sh | sh && \
+    mix local.hex --force && \
+    mix archive.install hex phx_new ${PHX_VERSION} --force && \
+    mix local.rebar --force
+
+ENV APP_HOME /app
+RUN mkdir $APP_HOME
+WORKDIR $APP_HOME
+
+EXPOSE 4000

.devcontainer/devcontainer.json

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+{
+	"name": "Phoenix",
+	"dockerComposeFile": "docker-compose.yml",
+	"service": "app",
+	"workspaceFolder": "/workspace",
+
+	// Set *default* container specific settings.json values on container create.
+	"settings": {
+		"terminal.integrated.shell.linux": "/bin/bash",
+		"sqltools.connections": [{
+			"name": "Container database",
+			"driver": "PostgreSQL",
+			"previewLimit": 50,
+			"server": "localhost",
+			"port": 5432,
+			"database": "postgres",
+			"username": "postgres",
+			"password": "postgres"
+		}]
+	},
+
+	// Add the IDs of extensions you want installed when the container is created.
+	"extensions": [
+		"dbaeumer.vscode-eslint",
+		"mtxr.sqltools",
+		"mtxr.sqltools-driver-pg",
+		"jakebecker.elixir-ls",
+		"mjmcloug.vscode-elixir"
+	],
+
+	// Use 'forwardPorts' to make a list of ports inside the container available locally.
+	// "forwardPorts": [],
+
+	// Use 'postCreateCommand' to run commands after the container is created.
+	// "postCreateCommand": "bash scripts/install.sh",
+
+	// Comment out connect as root instead. More info: https://aka.ms/vscode-remote/containers/non-root.
+	// "remoteUser": "node"
+}

.devcontainer/docker-compose.yml

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+version: '3'
+
+services:
+  app:
+    build:
+      context: .
+      dockerfile: Dockerfile
+      args:
+        VARIANT: latest
+        PHX_VERSION: 1.5.3
+
+    volumes:
+      - ..:/workspace:cached
+      - vscode-extension:/root/.vscode-server-insiders
+
+    # 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: node
+
+    # 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
+    environment:
+      POSTGRES_PASSWORD: postgres
+      POSTGRES_USER: postgres
+      POSTGRES_DB: postgres
+
+    # Add "forwardPorts": ["5432"] to **devcontainer.json** to forward MongoDB locally.
+    # (Adding the "ports" property to this file will not forward from a Codespace.)
+
+volumes:
+  postgres-data:
+  vscode-extension: