transforms: show header transforms in UI

I have created an action query like this

```
type Query {
""" Institutions by Specialty """ mt_institutions_by_specialty(
specialty_id: String!
): Institutions
}
```

Now I need to use that speciality_id input as a value in the Headers section bellow. But {{$body.input.speciality_id}} does not convert. It works only in the "Change Request Options" section.

Start by reproducing the action query and comparing the transform behavior in the Headers section with the Change Request Options section. Trace where the header value is evaluated; done when {{$body.input.speciality_id}} resolves in Headers as it already does in Change Request Options.

Written by the indexing model from the issue text.