Expose EventEnum in the docs and fix custom events example

[vfdev-5]

🚀 Feature

Currently, EventEnum is absent in the docs and below there is no link in the docs:

https://pytorch.org/ignite/master/engine.html#ignite.engine.events.Events

Idea is to introduce it in the docs by adding a docstring here

ignite/ignite/engine/events.py

Lines 144 to 145 in d384dc6

	class EventEnum(CallableEventWithFilter, Enum):
	pass

and improve above and all other examples where EventEnum is mentioned (please, search for it in the whole repository) by adding

from ignite.engine import EventEnum

For Hacktoberfest contributors, feel free to ask questions for details if any and say that you would like to tackle the issue.
Please, take a look at CONTRIBUTING guide.

[harsh8398]

I would like to work on this. Could you please assign this to me? Also one quick question, can you elaborate on improve above and all other examples where EventEnum is mentioned?

[vfdev-5]

@harsh8398 sure !

Also one quick question, can you elaborate on improve above and all other examples where EventEnum is mentioned?

Please, search for all EventEnum mentions in the repository. It should be mentioned in several docstrings and examples that probably missing an explanation on how to import EventEnum. Idea is to add from ignite.engine import EventEnum to all those examples.