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.

config_local.py

@@ -0,0 +1,12 @@
+PROXY_X_FOR_COUNT = 1
+PROXY_X_PROTO_COUNT = 1
+PROXY_X_HOST_COUNT = 1
+PROXY_X_PORT_COUNT = 1
+PROXY_X_PREFIX_COUNT = 0
+
+UPGRADE_CHECK_ENABLED = False
+CHECK_SUPPORTED_BROWSER = False
+ENHANCED_COOKIE_PROTECTION = True
+
+SESSION_EXPIRATION_TIME = 12 * 60 * 60
+MAX_SESSION_IDLE_TIME = 60 * 60