Introduce a tracker API and integrate Aimstack tracker

[dushyantbehl]

What does this PR do?

This pull request adds a tracker API to llama recipes and integrates Aimstack https://aimstack.io/ The goal of tracker API is to create a standard template to attach any other experiment trackers.

With aim integration there is a dependency on the aim package which needs to be installed separately before using this.

Fixes # (issue)

Relates to issue https://github.com/facebookresearch/llama-recipes/issues/225

#Before submitting

• [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• [x] Did you read the contributor guideline, Pull Request section?
• [x] Was this discussed/approved via a Github issue? Please add a link to it if that's the case. https://github.com/facebookresearch/llama-recipes/issues/225
• [x] Did you make sure to update the documentation with your changes?
• [ ] Did you write any new necessary tests?

Thanks for contributing 🎉!

[dushyantbehl]

Opening up the PR for initial review. Feature has to be fully tested and unit test and documentation fixed.

[dushyantbehl]

@HamidShojanazeri @nairbv opening this PR for feedback. Sorry it has been long and I have been occupied with other things. I have added a tracker API which can be used to add support for any tracker like WandB / Aim along with Aim integration.

[nairbv]

looks like there are conflicts with main that will have to be resolved too

[dushyantbehl]

@nairbv @HamidShojanazeri @chauhang I noticed a spell check was failing for this PR which is fixed now. Please take a look and let me know if anything else needs to be fixed.