tests: ipc_service: Test restarting session in different scenarios

This commit adds a test that checks if disconnecting
and restarting the IPC session works correctly. The
test is also focused on the "unbound" callback.

Signed-off-by: Dominik Kilian <Dominik.Kilian@nordicsemi.no>
Co-authored-by: Radoslaw Koppel <radoslaw.koppel@nordicsemi.no>