Add basic devcontainer setup

This is still missing testing for other PostgreSQL versions and CRDB. It
also doesn't setup testing for different connection types.

Author: jackc

.devcontainer/Dockerfile

@@ -0,0 +1,9 @@
+FROM mcr.microsoft.com/devcontainers/go:2-1.25-trixie
+
+RUN apt-get update && apt-get install -y postgresql-common \
+    && yes | /usr/share/postgresql-common/pgdg/apt.postgresql.org.sh \
+    && apt-get install -y postgresql-client-18 \
+    && rm -rf /var/lib/apt/lists/*
+
+USER vscode
+RUN go install golang.org/x/tools/cmd/goimports@latest

.devcontainer/devcontainer.json

@@ -0,0 +1,6 @@
+{
+	"name": "pgx",
+	"dockerComposeFile": "docker-compose.yml",
+	"service": "app",
+	"workspaceFolder": "/workspaces/${localWorkspaceFolderBasename}"
+}

.devcontainer/docker-compose.yml

@@ -0,0 +1,35 @@
+version: '3.8'
+
+volumes:
+  postgres-18-data:
+
+services:
+  app:
+    build:
+      context: .
+      dockerfile: Dockerfile
+
+    volumes:
+      - ../..:/workspaces:cached
+
+    environment:
+      PGUSER: postgres
+      PGPASSWORD: postgres
+      PGDATABASE: pgx_test
+      PGHOST: localhost
+
+    # Overrides default command so things don't shut down after the process ends.
+    command: sleep infinity
+
+  postgres-18:
+    image: postgres:18
+    restart: unless-stopped
+    volumes:
+      - postgres-18-data:/var/lib/postgresql
+      - ../testsetup/postgresql_setup.sql:/docker-entrypoint-initdb.d/01-setup.sql:ro
+    network_mode: service:app
+    environment:
+      POSTGRES_USER: postgres
+      POSTGRES_PASSWORD: postgres
+      POSTGRES_DB: pgx_test
+      POSTGRES_HOSTNAME: localhost