Bluetooth: Audio: Rename enum bt_audio_pac_type

The enum bt_audio_pac_type does not fully
represent the what the value is used for.

The typical use of it is not for just published
audio capabilities (PAC), but rather describes the
type, or direction, of audio endpoints.

For the unicast client, the type/direction is
relative to the unicast server.

Signed-off-by: Emil Gydesen <emil.gydesen@nordicsemi.no>