LeAudio: Postpone the bidirectional context alignment

We should be keeping the contexts individually for each
direction as long as possible and align the directions
with each other for the bidirectional contexts only when
the stream is being started in a bidirectional scenario.

This is mostly convenient for the sink metadata updates
that may come multiple times before the local sink is
resumed (if ever) and eliminates unnecessary alignment
with context that may never be resumed.

Test:  atest --host bluetooth_le_audio_client_test bluetooth_le_audio_test --no-bazel-mode
Change-Id: I46be6bc55dc8c608206dcea3f6caa17566507834