PR for Ihme/experiments

[nayana-wiai]

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[nayana-wiai]

@ayushdeva-ai @avtansh1317 @sansiddh This PR is somewhat ready. Please take a look and provide feedback. Here are the key points:

• The IHME config is now quite similar to SEIR.
• The IHME model is internally quite different from SIR but the fitting.py script mirrors the one for SIR, and much of the utils, plotting etc. overlap.
• There are new scripts to run the IHME and SEIR models.
• There are still some TODOs scattered throughout the code which I'll be addressing.
• There is a driver config in configs/other/ (can be renamed) which can be used to generate multiple configs to run experiments. I personally found this useful for hyperparameter tuning and multiple train period experiments.
• Ignore any function called create_output, it just dumps out all components of predictions_dict individually and will be removed before merging.
• This PR does not have any scripts which combine IHME and SEIR, that will be in a separate PR.