Improve local development setup

[JordiParraCrespo]

Improve local development setup

Summary

• Add network-specific Make targets (start-testnet, start-mainnet and their -clean variants) for one-command startup
• Add database management commands (db-schema-drop, db-schema-apply, db-schema-reset, db-shell, db-tables, db-size) to interact with the database without restarting Docker containers
• Rework start-clean to use db-schema-reset instead of docker compose down -v for faster resets
• Add configs/ directory with pre-configured testnet-config.yaml and mainnet-config.yaml
• Rework README.md with improved documentation: manual vs automated start flow, configuration, database management, services, and troubleshooting
• Fix Hasura ACTION_BASE_URL port alignment with Callisto Actions config
• Note mint module exclusion (not used in XRPL EVM Sidechain)