Add 'Use Broadcast' sync option to send UDP audio data

[netmindz]

This pull request adds support for using subnet broadcast instead of multicast when sending audio sync packets, providing more flexibility for network configurations. It introduces a new audioSyncBroadcast option, updates the configuration and UI to support this, and ensures the new setting is properly saved and restored.

This is useful as a work around for networks that do not support multicast properly and does also appear to help multiple devices actually receive the data at the same time in some cases (some WIFI networks turn multicast into unicast)

Network transmission improvements:

• Added a new audioSyncBroadcast flag to allow sending audio sync packets to the subnet broadcast address instead of using multicast. The code now computes the broadcast address and sends packets accordingly when this option is enabled. (audio_reactive.h, [1] [2]

Configuration and persistence:

• Updated the sync configuration to include the new broadcast option, ensuring it is saved to and loaded from the configuration JSON. (audio_reactive.h, [1] [2]

User interface enhancements:

• Updated the UI to display information about the new broadcast option in the sync settings, making it clear to users when broadcast is being used instead of multicast. (audio_reactive.h, audio_reactive.hL3204-R3218)