feat: Add config option for payload on bridge notification

[jmrt47]

Summary

Add support for custom bridge notification payloads with the new config options:

• notification_payload_up
• notification_payload_down

This allows bridge state notifications to use configurable payload values, including values with spaces, instead of the default payloads. Config is optional and defaults to the previous values 1 and 0.

This partially implements: #214

Changes

• Added config parsing for notification_payload_up and notification_payload_down
• Updated bridge notification handling to publish the configured up/down payloads
• Added broker test coverage for the new behavior
• Updated config/docs examples

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