Upgrade XgBoost to 1.7.x (#362)

* Upgrade XgBoost version to 1.7.3

* Restructure checkpointing.py and fix Unit tests

* Resolve Flake8 style errors

* Address Comments and improvements

* Add comments and improvements

* Upgrade xgboost to 1.7.4

* remove grow_local_histmaker and Single precision histogram

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Co-authored-by: Malav Shastri <malavhs@amazon.com>

Reverting numpy 1.21.2 to 1.19.2 and adding regression (#300)

reverting numpy to 1.19.2 and adding regression

Co-authored-by: Nikhil Raverkar <nraverka@amazon.com>

Adding new objective metrics to 1.3-1 version (#296)

Fix JSON output format (#281)

Fix xgboost 1.2-1 codebuild (#261)

Bump requirements versions to fix security vulnerabilities (#182)