Camera: Pass an executor during the extension characteristics service bind call

Camera extensions characteristics will bind to the camera extensions
proxy service without passing a dedicated executor for the connection
callbacks. In this case, the callbacks will be called in the main thread
which can be problematic for clients using the same thread.

Bug: 191192317
Test: Camera CTS
Change-Id: Ic952edd766d26016b6203c84d067a6b1061ed090