Custom gate filter for noise model

[lqtmirage]

• Allow users to specify the condition for applying noise to the gate with a user defined function when adding NoiseInstruction to NoiseModel by add_noise() method.
• The other applicable conditions of NoiseInstruction and the custom condition are connected by AND.
• If the noise model has no custom conditions, the cost during noise search for a gate is only single check that the dictionary is empty.

Examples

model = NoiseModel()

# If custom_gate_filter argument is omitted, it remains the same as before.
model.add_noise(BitFlipNoise(0.004, [], [names.H, names.X]))

# Works only on 2 qubit gates.
model.add_noise(
    PhaseFlipNoise(0.003, [], []),
    lambda gate: len(gate.target_indices) + len(gate.control_indices) == 2,
)

# Acting on qubit index 3 of a gate with 1 target qubit and 1 control qubit.
model.add_noise(
    DepolarizingNoise(0.002, [3], []),  # Targeting qubit index 3.   
    lambda gate: len(gate.target_indices) == 1 and len(gate.control_indices) == 1,
)

[github-actions]

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