### Description

I would love to make this an error, but we have had a duplicate key in
`targets.json` for a while now. Instead, we're merging in a semi-smart way.
This will allow you to have things like `"target.features_add"` twice, and
both will take affect.

### Pull request type

    [x] Fix
    [ ] Refactor
    [ ] Target update
    [ ] Functionality change
    [ ] Docs update
    [ ] Test update
    [ ] Breaking change