Creates a tfl.layers.Linear layer initialized to be an average.

linear_input Input to the linear layer.
feature_configs A list of tfl.configs.FeatureConfig instances that specify configurations for each feature.
model_config Model configuration object describing model architecture. Should be one of the model configs in tfl.configs.
weighted_average If the linear coefficients should be positive and sum up to one.
submodel_index Corresponding index into submodels.
dtype dtype

A tfl.layers.Linear instance.