audio: Add libaudioclient tests to postsubmit for the AIDL HAL

These framework-side tests are helpful in detecting breakages
caused by changes in the HAL code.

Add to postsubmit first because the presubmit check does not
allow adding to presubmit without accumulating some history first.

Bug: 311830316
Test: atest
Change-Id: I1f946c71a89117d25f39fde34877988ea7e1d466