Added support hardswish function

[shaharelys]

Before submitting

• [x] Was this discussed/approved via a Github issue? Yes, #92
• [x] Did you read the contributor guideline, Pull Request section? Yes btw, the url should be fixed to 'https://github.com/Lightning-AI/pytorch-lightning/blob/master/.github/CONTRIBUTING.md'.
• [ ] Did you make sure to update the docs? Not yet
• [x] Did you write any new necessary tests? Yes, only in opinfo.py

What does this PR do?

Implements the HardSwish activation function.

Fixes #92

PR review

This PR is open for review, though I'm not entirely certain it's 100% complete, as this is my first contribution. All tests have passed, but docs has not been updated. Feedback from the community is welcomed!

Did you have fun?

Yes! 🙃