Add keras-tuner like interfaces for Hyperparam optimization

[AvinashBukkittu]

Keras-tuner (https://github.com/keras-team/keras-tuner) is a hyperparameter tuner for tf.keras. We like to take insights from this framework. In particular, we like to design the following interface in our framework

1. Develop and expose a Hyperparam class like TPE, Hyperband etc to the user. The user supplies the objective_func while creating this object something like

tuner = TPE(
    objective_func,
    objective='val_accuracy',
    max_trials=5,
    executions_per_trial=3,)

2. The user invokes hyperparameter search by calling search()

tuner.search()

3. The user can get results through the following utility functions

models = tuner.get_best_models(num_models=2)

or

tuner.results_summary()

In addition, we may like to provide pre-made tunable applications like they do in keras-tuner.