Adding mlflow logging functionality to yolox

[Im-Himanshu]

Needed integration of yolox to log experiments with mlflow, for that created this pull request that create another option in -l --logger argument to be "mlflow".

works on environment file (.env) in the root folder of the projects.

required additional dependency of mlflow and python-dotenv failing which error is raised if logger is set to mlflow.

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1 out of 2 committers have signed the CLA.

✅ Im-Himanshu
❌ jgoyalh1

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[Im-Himanshu]

committed with wrong username, deleting to push in different pull request.