wip: Initial include support

[lu-zero]

Here what I'd propose for adding the ability to reuse some hurl file fragment over others

• Have a Directive that can be intermixed with Entry syntax element
  • Have an [Include] directive with a path that must be another hurl file
• Add a fn resolve(context: Context) that produces a new HurlFile with all the directives resolved

Usage wise resolve() needs to know what is its root base and pass it down so every hurl files that gets included.
It will need some mechanism to detect inclusion cycles so the Context will have to keep track on where it is.

Fixes #2110 and #317

[jcamiel]

Ho @lu-zero

Thanks for your PR but unfortunately, we have decided to postpone working on include: we think implementation is probably hard, syntax has to be decide, and some things needs to be discuss (cycle, error displays etc.) if yet we choose to add it.

[lu-zero]

Oh well, I guess you can use this as discussion/starting point.

Implementation wise, even if I had to get accustomed to your codebase, didn't feel too hard.