Add the possibility to create import file names dynamically

[NicholasPini]

Is your feature request related to a problem? Please describe. I'm trying to build a Nickel file which contains info about a bunch of Python projects in a monorepo and it would be nice to be able to read the prproject.toml files into a Nickel record. The issue is that I already have a field which contains the path to the project, and this would cause repetition:

{
  project_path = "path/to/project"
  toml_content = import "path/to/project/pyproject.toml"
}

Describe the solution you'd like It would be nice if the string passed to the import keyword could be constructed at runtime, enabling something like this:

{
  project_path = "path/to/project"
  toml_content = import "%{project_path}/pyproject.toml"
}

Describe alternatives you've considered

1. Repeat the path in two strings, which is a bit annoying and error prone.
2. Extract the pyproject.toml into whatever script the Nickel file is fed into. Kind of defeats the purpose of using Nickel in the first place.

[yannham]

Note: related or even duplicate of https://github.com/tweag/nickel/issues/1865

[NicholasPini]

Sorry, you're right. I'll let you decide if it makes sense to keep this issue open just to show my use case, or if it's just an hassle and it's better to close it.

[yannham]

No worries, I just wanted to link to the other issue before I forget. I think we can keep this one open as well; I find the feature request to be formulated more clearly, so other people might find it before the oldest.