Add possibility to pass arguments between stages or set build-level environment variables in Rancher Pipelines

[dawid-szmigielski-gaincapital]

What kind of request is this (question/bug/enhancement/feature request):
Enhancement

Steps to reproduce (least amount of steps as possible):
Currently it is not possible to pass arguments between stages (each stage is independent), or set custom environment variables that would be visible in all stages. Adding this can prove useful in a lot of scenarios.

Example:
User has to calculate new version number based on the last tag in the repo, so he can tag the image correctly. At the moment this is not possible as in "Build and Publish Image" step type you have to pass static "Image Name" which can resolve only pre-configured Rancher Pipeline variables.

Result:
Steps can generate outputs that can be consumed by further stages,
OR
it is possible to set environment variables in "Run Script" step, that are injected into all following stages.

Environment information

Rancher v2.3.3