CmdRunner guide (#8592)

* initial commit

* wip

* WIP

* progressing

* remove copied part

* progressing

* document as_func()

* complete docs about arg formatting

* add PythonRunner documentation

* fix markup

* improve markup

* multiple changes

- revamp the cmd_runner_fmt doc
- add CmdRunner instance and context parameters
- changed formatting of other blocks

* fix typo + reduce tables sizes

* improve text

* fixes and adjustments

* fix sanity

* fix version added

docs/docsite/extra-docs.yml

@@ -18,3 +18,4 @@ sections:
     toctree:
       - guide_deps
       - guide_vardict
+      - guide_cmdrunner