Add initial setup for pgAdmin 4 with Docker and Nginx Proxy Manager

- Created .env.example for environment variable configuration.
- Added .gitignore to exclude sensitive files.
- Introduced config_local.py for pgAdmin settings.
- Added docker-compose.portainer.yml for service orchestration.
- Created Dockerfile for custom image building.
- Added README.md with setup instructions and usage guidelines.
- Included servers.json as a template for PostgreSQL server connections.

.env.example

@@ -0,0 +1,14 @@
+TZ=Europe/Moscow
+
+PGADMIN_DEFAULT_EMAIL=admin@example.com
+PGADMIN_DEFAULT_PASSWORD=change-this-password
+PGADMIN_PUBLISHED_PORT=5050
+PGADMIN_VOLUME_NAME=pgadmin_data
+
+PGADMIN_CONFIG_SERVER_MODE=True
+PGADMIN_CONFIG_MASTER_PASSWORD_REQUIRED=True
+PGADMIN_CONFIG_ENHANCED_COOKIE_PROTECTION=True
+PGADMIN_CONFIG_UPGRADE_CHECK_ENABLED=False
+
+NPM_NETWORK=npm_proxy
+PGADMIN_DOMAIN=pgadmin.example.com