BackendPatternConfig
set_fuser_method(fuser_method)
  Set the function that specifies how to fuse this
  BackendPatternConfig's pattern.

  The first argument of this function should be *is_qat*, and the
  rest of the arguments should be the items in the tuple pattern.
  The return value of this function should be the resulting fused
  module.

  For example, the fuser method for the pattern *(torch.nn.Linear,
  torch.nn.ReLU)* can be:

     def fuse_linear_relu(is_qat, linear, relu):
        return torch.ao.nn.intrinsic.LinearReLU(linear, relu)

  For a more complicated example, see https://gist.github.com/jer
  ryzh168/8bea7180a8ba3c279f2c9b050f2a69a6.

  Return type:
     *BackendPatternConfig*

set_observation_type(observation_type)
  Set how observers should be inserted in the graph for this
  pattern.

  Observation type here refers to how observers (or quant-dequant
