Add functionality to merge 'other' category of an item

[LDSamson]

In our case, we often have items that give additional explanation about an item, for example about why an item is missing, or why a drug is not administered. These columns are tightly coupled to one specific item, and are often empty unless certain conditions are met.

It would be quite helpful if we add this functionality for us since it occurs often.
Basic idea is that we define which items should be paired to others in the metadata, something like this:

And then a function will merge both items into one so that the value is something like: