input: Write a function to generate and plot a linear function y = 2x + 3 using matplotlib.
  assert plot_linear_function() is None
output: def plot_linear_function():
      import matplotlib.pyplot as plt
      import numpy as np
  
      x = np.linspace(-10, 10, 400)
      y = 2 * x + 3
  
      plt.plot(x, y, label='y = 2x + 3')
      plt.xlabel('x')
      plt.ylabel('y')
      plt.title('Plot of the linear function y = 2x + 3')
      plt.legend()
      plt.grid(True)
      plt.show()