[Feature] A Checkpoint hook for saving model checkpoints as Weights & Biases Artifacts

[soumik12345]

Motivation

Fixes #1492

Modification

The PR adds a mmengine.hooks.WandbCheckpointHook that can act as a drop-in replacement for mmengine.hooks.CheckpointHook that enables us to periodically save our model checkpoints as W&B Models Artifact.

Checklist

1. Pre-commit or other linting tools are used to fix the potential lint issues.
2. The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
3. If the modification has potential influence on downstream projects, this PR should be tested with downstream projects, like MMDetection or MMPretrain.
4. The documentation has been modified accordingly, like docstring or example tutorials.

[CLAassistant]

All committers have signed the CLA.