Further develop usage of static user config

[benedikt-voelkel]

This concerns the static configuration in the config.yaml in the recipes.
See for instance https://github.com/benedikt-voelkel/o2tunerRecipes/blob/main/transport_cut_optimisation/config.yaml#L1

• introduce a well-defined top key under which the user is allowed to have several sub-keys for configurations
• make it possible to use variables from these configurations also in shell commands and not only in the python scripts. This enhances the usage of shell commands which otherwise would need to be wrapped in python scripts by the user. It has an obvious use case in the transport cut optimisation and beyond.
• demonstrate its use case with transport cut optimisation

Example

config:
  default_config: &default_anchor
    par1: 5
    par2:
      sub_par: 1
  dev_config: &dev_anchor
    par1: 4
    par2:
      sub_par: 2

stages_user:
  my_stage:
    cmd: echo :default_config.par1:

  my_stage_dev:
    cmd: echo :dev_config.par2.sub_par:

  some_python_stage:
    python:
      file: my_python.py
      entrypoint: run
      config: *default_anchor