DeepProfiler produces incorrect crops if provided with images of different sizes

In profiling mode, if provided with images of different sizes than the specified in the config (in `config["dataset"]["images"][{"width", "height"}]`), DP will silently generate incorrect crops.

I think the issue comes from [`get_cropping_regions()`](https://github.com/cytomining/DeepProfiler/blob/master/deepprofiler/imaging/boxes.py#L121-L122), where the config-specified image size is used to normalise the bounding indices. Note that there's no exception raised when the input image mismatches the specified shape.

I also think the [docs](https://cytomining.github.io/DeepProfiler-handbook/docs/03-images.html) are slightly confusing, as it's mentioned:

> The size of images is, in principle, flexible and DeepProfiler can work with different resolutions and image dimensions.

Please correct me if I'm wrong, but I think this is the only reason making DeepProfiler incompatible with images of variable size (for profiling) and could easily be solved by reading the image dimensions dynamically. I opened a PR to implement just that - https://github.com/cytomining/DeepProfiler/pull/354.

It'd be great if you could also update the docs to clarify how DeepProfiler handles images of variable size in training vs. profile mode.