tests: bluetooth: tester: Add PBP support

Implements the PBP commands of the BTP specs, in order to support
testing the PBP through autopts. This PR is in conjunction with the
following PR in AutoPTS: https://github.com/auto-pts/auto-pts/pull/1356



Signed-off-by: Frode van der Meeren <frode.vandermeeren@nordicsemi.no>