Liquid testing: support different YAMLs like different parts in Liquid templates

[robindeclercq]

Is your feature request related to a problem? Please describe.
Request from our partners Fintrax - where they'd like to have different parts for each case since the YAMLs become huge and hard to maintain. Similar to Liquid code parts.

Describe the solution you'd like
Solution should be in VS code.

Describe alternatives you've considered

Additional context
Add any other context or screenshots about the feature request here.

[MelSFNL]

@robindeclercq new use case at it is easier from a git perspective to be able to create different parts (= different files). This will mean less time spent on puzzling out "merge conflicts" which aren't even real conflicts but just two people creating tests on the same template and around the same YAML line number range