Command references outside the generated module

Some MAPDL commands are not defined in the generated module (``pyconverter-generatedcommand``) but are well defined outside of it when adding it to the PyMAPDL package.

It is the case with ``FILE``: it is not defined in ``_commands`` (= generated module) but it in ``mapdl-grpc.py``.

Adding an option in the configuration to add "manual" references in the ``_commands`` submodule would fix this issue:

```
commands_already_defined:
- "INITIAL_MAPDL_COMMAND": "python_name"
- "FILE": "file"
```

Start by tracing how the configuration produces the ``_commands`` generated module and compare it with the existing ``FILE`` definition in ``mapdl-grpc.py``. Check how ``pyconverter-generatedcommand`` handles manually defined commands, then verify that a configuration entry such as ``commands_already_defined`` produces the expected references without duplicating existing definitions.

Written by the indexing model from the issue text.