input: Write a python function to check if a given point is within a geo-fence.
  assert is_within_fence((51.5074, -0.1278), 10) == True
  assert is_within_fence((40.7128, -74.0060), 15) == False
  assert is_within_fence((34.0522, -118.2437), 5) == True
output: def is_within_fence(point, radius):
      from geopy.distance import geodesic
  
      # Center of the geo-fence (example coordinates)
      center = (51.5074, -0.1278)  # Example: Center of London
      
      # Calculate the distance between the center and the point
      distance = geodesic(center, point).kilometers
      
      # Check if the distance is within the radius
      return distance <= radius