Support model with no-named inputs/outputs

OTBTF should handle a model that doesn't name inputs/outputs, e.g. a model created like that :

import tensorflow as tf
# Input
x1 = tf.keras.Input(shape=[None, None, 4])  # [h, w, N]
x2 = tf.keras.Input(shape=[None, None, 4])  # [h, w, N]

# Compute multiply
y = tf.math.multiply(x1, x2)

# Create model
model = tf.keras.Model(inputs=[x1, x2], outputs=y, name="multiply")
model.save("my_model_multiply")

When running TensorflowModelServe, the user could ommit the source#.placeholder and output.names arguments