[Feature Request] Add LoadImageFromNdarray alias for LoadImageFromWebcam

[GeorgePearse]

Original issue: open-mmlab/mmdetection#7171
Created: 2022-02-16
Last updated: 2022-02-17

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Describe the feature

Motivation
LoadImageFromWebcam is not easy to understand how it works.
Actually it transform ndarray to default mmdetection data format.

So I think it is good idea to add alias as LoadImageFromNdarray.
implementation will be like just below

# end of the mmdet.datasets.pipelines.py
LoadImageFromNdarray = LoadImageFromWebcam

If it seems good idea, I will create the PR.