Implement the GroupDataProvider

[jepenven-silabs]

Problem

We only have an example implementation of the GroupDataProvider. We need to have at least one basic implementation that allows trial decryption of incoming group message and encryption of group message. This implementation can and should be overridden to allow the use of platform specific cryptographic api.

Proposed Solution

Convert the GroupDataProvider class from pure virtual to virtual class as to provide a common implementation of its feature.

Related issues :

• Add / remove group key [Secure Channel] 1-N Traffic - Group Keys - Remove group key #1820

While doing so please apply @bzbarsky-apple comments for PR #10985 :

• StaticGroupsProvider::Decrypt should take the PacketHeader as a const reference, not by value.
• StaticGroupsProvider::Decrypt should almost certainly take the PacketBufferHandle as an lvalue reference, not an rvalue reference, since it's not taking ownership of the buffer, I assume.