Set TensorBoard callback by default when calling model.fit() with Keras

[arjuninv]

When calling Keras's model.fit(), create a TensorBoard callback instance and pass it by default.

Example:

log_dir="logs/fit/" + datetime.datetime.now().strftime("%Y%m%d-%H%M%S")
tensorboard_callback = tf.keras.callbacks.TensorBoard(log_dir=log_dir, histogram_freq=1)

model.fit(x=x_train, 
          y=y_train, 
          epochs=5, 
          validation_data=(x_test, y_test), 
          callbacks=[tensorboard_callback])