LeAudio: Support multiple contexts in stream metadata

This properly handles multiple context and multiple CCIDs when
metadata is prepared. It does that by renameing one of the member
to better indicate that this particular context is used for selecting
the right set configuration, but adds another member holding multiple
contexts so they could be used in the stream metadata and use proper
CCID list.

Bug: 240145685
Test: atest --host bluetooth_le_audio_test bluetooth_le_audio_client_test bluetooth_test_broadcaster_state_machine bluetooth_test_broadcaster --no-bazel-mode
Change-Id: Ieb53ce2ddd5aad5f32a7c808900db6608c5dc0d4