Field identifying inputs/ouput types to prevent operations on rgb stack ( and perhaps future ) output images

[LTDakin]

Problem:
Currently there's nothing in the UI stopping you from trying to do a median on a rgb stack output. Only issue is that RGB outputs are 3d fits files with channels for Red, green, and Blue. Median's and other operations should be blocked from using colored images as input.

Discussion:
We need to add some identifier/tag/metadata to RGB outputs that we can filter for when displaying operation input options. So this isn't a one off fix, we should consider other cases where we might need to tag images (input or output) and coming up with a way of implementing/naming this extra field. Or at least implement it in a way that can be reused.

Solutions:

• broad: field "type" with string value on datalab inputs/outputs
• minimal: field "color" with boolean value