input: Write a function to generate a voltage signal with random noise. The function should take the frequency and amplitude as inputs and return the noisy signal.
  import numpy as np
  
  assert generate_noisy_signal(250, 1) == np.sin(2*np.pi*250*np.linspace(0, 1, 1000)) + np.random.normal(0, 0.1, 1000)
  assert generate_noisy_signal(500, 0.5) == np.sin(2*np.pi*500*np.linspace(0, 1, 1000)) + np.random.normal(0, 0.1, 1000)
  assert generate_noisy_signal(1000, 2) == np.sin(2*np.pi*1000*np.linspace(0, 1, 1000)) + np.random.normal(0, 0.1, 1000)
output: def generate_noisy_signal(frequency, amplitude):
      t = np.linspace(0, 1, 1000)
      signal = amplitude * np.sin(2 * np.pi * frequency * t)
      noise = np.random.normal(0, 0.1, 1000)
      return signal + noise