SCQT Tutorial 2: required changes

The following changes were required in SCQT to succesfully run tutorial 2 with the QM backend:

1. BATCHED_FREQ_BACKENDS = ["qblox", "mock", "quantum_machines"] in meas.spectroscopy
2. max_batch_size=min(50, max_batch_size(qubit, frequencies, "readout")), in cal.spectroscopy.calibrate_resonator_frequency