bug: Missing on_save() event in callback.py

[seshapad]

Describe the bug

There is no callback available for on_save event in the trainer controller callback.

Platform

Please provide details about the environment you are using, including the following:

• Interpreter version:
• Library version: [X]

Sample Code

NA

Expected behavior

Any operation registered with on_save trigger or metric registered with it should work.

Observed behavior

on_save is not available in callback.

Additional context

Add any other context about the problem here.