Update CometCallback to allow reusing of the running experiment
Author: Lothiraldan
Pull request: yes

# What does this PR do?

Update CometCallback to allow reusing of the running experiment.

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- [ ] Did you write any new necessary tests?


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Comments:
Hi @Lothiraldan, thanks for opening a PR! Let us know when it's ready for review. 

cc @muellerzr 

Hi @amyeroberts, I wanted to open a PR in our fork for internal review first. Sorry about the noise.

I can close this one, reopen one in our fork or leave this one open and have the comments shared internally, let me know what would works best for you.

The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_31366). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

@Lothiraldan Any of the options work for us. We can leave this open until your internal review has happened, this PR has been updated to reflect the review and then you can just ping us when it's ready :) 

@amyeroberts Hi, this PR is now ready for a review. Sorry for the delay, the internal reviews highlighted some potential improvements that took a bit of time.