Fix OsSignal for GracefulShutdown, fix default shutdown.timeout in docs

[alexlapa]

Resolves #29

Synopsis

1. Wrong default shutdown.timeout config.toml
2. Handler for GracefulShutdown do not send messages to sub

Checklist

• Created PR:
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• Documentation is updated (if required)
• Tests are updated (if required)
• Changes conform code style
• CHANGELOG entry is added (if required)
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