Convenient ways to merge/concatenate/combine multiple configurations

[keller-mark]

Easy_vitessce provides convenient ways to create Vitessce configurations with one (or just a few) views using the convenient scanpy/spatialdata-plot APIs.

We should then make it easy to combine multiple of these configs (with just a few views each) into a larger grid of views that can still be represented using a single Vitessce configuration. This would make easy_vitessce more useful as a way to incrementally build up more complex Vitessce configurations (e.g., for deploying in website/data portal contexts).