Fix: Ensure Home Assistant discovery messages are always retained

[syssi]

Fix: Ensure Home Assistant discovery messages are always retained

Problem

Home Assistant requires MQTT discovery messages to be sent with the retained flag set to true for proper device discovery. Currently, the global enableRetain setting in MQTT configuration affects all messages, including discovery messages. When users disable enableRetain to prevent sensor values from being retained, Home Assistant discovery stops working because discovery messages are no longer retained.

Solution

This PR modifies the publish() function in pubMqtt.h to ensure that Home Assistant discovery messages (topics starting with homeassistant/) are always sent with retained=true, regardless of the global enableRetain setting.

Changes

• Modified pubMqtt.h lines 238-243
• Added logic to force retained=true for discovery messages after the global retain check
• Preserves existing behavior for all other MQTT messages

Testing

• Discovery messages are now retained on MQTT broker even when enableRetain is disabled
• Regular sensor data respects the enableRetain setting as before
• Home Assistant device discovery works regardless of retain configuration

Backward Compatibility

This change is fully backward compatible. Users who have enableRetain enabled will see no change in behavior. Users who have it disabled will now have working Home Assistant discovery without needing to enable retain for all messages.

Fixes Home Assistant integration when enableRetain is disabled.