Add support for custom payloads and channels in broadcasting

[JanneDeVos]

This pull request introduces support for broadcasting events to multiple channels and connections with specific payloads for each connection. The changes include:

BroadcastEvent Class Enhancements:

• Added methods to handle broadcasting to multiple connections and channels.
• Implemented logic to format and send payloads specific to each connection.

Test Cases:

• Added new test cases in BroadcastEventTest to verify the functionality of broadcasting to multiple channels and connections.
• Ensured existing tests are updated to reflect the new broadcasting logic.