Multicast Message sending

[jepenven-silabs]

Problem

Need a way to send group message with chip-tool.

Proposed Solution

As discussed with @bzbarsky-apple at least the following items need to be done

• Update WriteHandler to handle messages without endpointId but with Group
• Update WriteClient to handle messages without endpointId but with Group
• Update the Associate function from the ClusterBase class to use Group info instead of endpoint
• Update SessionManager and other as to allow Group session (e.g, bypass or modify GetSecureSession )

[jepenven-silabs]

Issue was done a long time ago without being closed. closing it now.

[jepenven-silabs]

Can execute Test to A commissioned device by executing :

./connectedhomeip/out/chip-tool/chip-tool tests TestGroupMessaging <nodeid>