Add support for custom bot configuration using mwbot.toml
- Added BotConfig struct in ot_config.rs to handle bot configuration.
- Implemented get_custom_config method in BotConfig to retrieve custom configuration in a type-safe manner.
- Updated main.rs to read and parse mwbot.toml file, and retrieve custom configuration.
- Added necessary dependencies (serde and oml) to Cargo.toml.- Created mwbot.toml file with example custom configuration.