Add Group Message Processing Test case

[jepenven-silabs]

Problem

We don't have any complete test for Group Messages

Proposed Solution

Add a Group Message Test inside the yaml test suite.

This test should do the following :

• Send a Groupcast write to device
• Send a Unicast read to verify if the group write operation was successful.
• Send another Groupcast write to check if the Group Message counter is working
• Send another Unicast read to verify the Groupcast write.

[jepenven-silabs]

Is blocked by #11078