Added links to all the metric files

[sayantan1410]

Fixes #2437
Opened this PR as an extension of this PR #2468, I by mistake lost track of that branch. Apology or the inconvenience. Extremely sorry.
@vfdev-5 @DevPranjal Kindly let me know if the changes are alright for you or I have made some mistake.

Check list:

• Documentation is updated (if required)

[vfdev-5]

@sayantan1410 thanks for the PR !

Actually, I think we decided a bit too fast about including this text to defaults.rst as now it is associated with metrics, however, we are also using it for certain handlers:

https://deploy-preview-2474--pytorch-ignite-preview.netlify.app/generated/ignite.handlers.param_scheduler.create_lr_scheduler_with_warmup.html#ignite.handlers.param_scheduler.create_lr_scheduler_with_warmup

@sayantan1410 @DevPranjal Any ideas how to deal with that ?

[sayantan1410]

@vfdev-5 There are two solutions in my mind :

1. Either to add the text to all the metric docstring individually, basically the one we rejected earlier.
2. To create another rst file like default.rst and include it in only the metric docstrings. And remove the previous default.rst from the metric docstrings.
   The default.rst will not have the text while the default_metric.rst will have the text and rest everything will be similar.

[vfdev-5]

In Idea (2) there could be few difficulties like those we had with defaults.rst (we have to copy it into a specific path to be discovered), we have to ensure that python definitions aren't duplicated and we still have to update all docstring for metrics to rename defaults.rst -> default_metric.rst.

Idea (1) is more explicit but can be a pain to do...

[sayantan1410]

@vfdev-5 Not really, I will just have to copy and paste the text to all the metric docstrings !!
Let's wait for @DevPranjal 's thoughts and then we can move forward with this I think.

[DevPranjal]

With the above issue, Idea 1. sounds good to me

[sayantan1410]

@vfdev-5 Hey, I have added the text for all the metric.py files listed here - https://pytorch.org/ignite/metrics.html#complete-list-of-metrics. Let me know if I have missed any.

[vfdev-5]

@sayantan1410 I provided a temporary CI fix: #2477
Once it is merged please sync your PR with master and we can land it.

[vfdev-5]

Thanks for the PR @sayantan1410

[sayantan1410]

@vfdev-5 hey, some checks were unsuccessful that's why it did not merge, can you check once why ??

[vfdev-5]

@sayantan1410 yes, there is an issue with new release of openai gym and deprecated env cartpole. we have to fix it.

[vfdev-5]

I think I can merge your PR as failures are unrelated.

[sayantan1410]

@thanks for closing the PR !!

[vfdev-5]

@sayantan1410 can you please open an issue describing the failed tests and maybe a fix ?

[sayantan1410]

@vfdev-5 yeah sure I will do it.