Hera runner debug log mode

[elliotgunton]

Is your feature request related to a problem? Please describe.
Hard to debug errors that occur in the runner itself

Describe the solution you'd like

• Setting an env variable e.g. hera__debug_mode to allow logging debug info during the Hera Runner setup.
• Users can then send us logs if the bug is with the runner

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.
N/A

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

Error log that motivated this issue (when trying out Pydantic IO):

Traceback (most recent call last):
  File "/opt/lib/python3.9/runpy.py", line 197, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/opt/lib/python3.9/runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "/layers/...pip/requirements/lib/python3.9/site-packages/hera/workflows/runner.py", line 493, in <module>
    _run()
  File "/layers/...pip/requirements/lib/python3.9/site-packages/hera/workflows/runner.py", line 481, in _run
    result = _runner(args.entrypoint, kwargs_list)
  File "/layers/...pip/requirements/lib/python3.9/site-packages/hera/workflows/runner.py", line 423, in _runner
    kwargs = _map_argo_inputs_to_function(function, kwargs)
  File "/layers/...pip/requirements/lib/python3.9/site-packages/hera/workflows/runner.py", line 259, in _map_argo_inputs_to_function
    map_runner_input(param_name, func_param.annotation)
  File "/layers/...pip/requirements/lib/python3.9/site-packages/hera/workflows/runner.py", line 240, in map_runner_input
    matched_field = map_field(field)
  File "/layers/...pip/requirements/lib/python3.9/site-packages/hera/workflows/runner.py", line 235, in map_field
    mapped_kwargs[field] = json.loads(kwargs[field])
  File "/opt/lib/python3.9/json/__init__.py", line 346, in loads
    return _default_decoder.decode(s)
  File "/opt/lib/python3.9/json/decoder.py", line 337, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/opt/lib/python3.9/json/decoder.py", line 355, in raw_decode
    raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)
time="2024-02-20T14:54:47 UTC" level=info msg="sub-process exited" argo=true error="<nil>"
Error: exit status 1

Meaning the string value being decoding was None, but the Python code used was:

# ...imports...

class MyInput(RunnerInput):
    """A pydantic model."""

    my_param: str = ""


@script(constructor="runner")
def echo_my_param(my_input: MyInput) -> None:
    """Prints out a message."""
    print(my_input.my_param)


def get_workflow_template() -> WorkflowTemplate:
    """Create and return the test-runner-input WorkflowTemplate."""
    global_config.experimental_features["script_pydantic_io"] = True
    make_scripts_runnable()
    with WorkflowTemplate(
        name="test-runner-input",
        entrypoint="steps",
    ) as wt:
        with Steps(name="steps"):
            echo_my_param(arguments={"my_param": "Hello world"})
        return wt