Added support for downloading wandb artifacts in the WandbLogger

[manangoel99]

What does this PR do?

This PR adds two functions to the WandbLogger, download_artifact and use_artifact.

The download_artifact function downloads the artifact from the given artifact path. If there is an ongoing run, the artifact is automatically linked to the run and otherwise it is just downloaded and stored. It returns the path to the downloaded artifact.

The use_artifact function links the artifact to the ongoing run and returns a wandb.Artifact object which can then optionally be downloaded by the user.

Fixes #11769

Does your PR introduce any breaking changes? If yes, please list them.

None

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