Better get_parameter/get_artifact support

[elliotgunton]

A goal of Hera should be to avoid the use of Argo expression syntax for Parameters and Artifacts, as without seeing the yaml itself it's not obvious what the keys are. E.g in the script_auto_infer example, a good syntax for the artifact would be:

    with DAG(name="d"):
        p = produce()
        c = consume(arguments=Artifact(name="i", from_=p.get_artifact("result")))
        p >> c

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Currently, there's no Hera syntax for fetching a Workflow argument, example taking inspiration from https://argoproj.github.io/argo-workflows/workflow-inputs/

@script(constructor="inline")
def echo(message: str) -> None:
    print(message)

with WorkflowTemplate(
    name="my-wt-with-args",
    entrypoint="main",
    arguments=[
        Parameter(name="arg-1"),
        Parameter(name="arg-2"),
    ],
) as wt:
    Steps(name="main"):
        echo(
            name="test",
            arguments={
                "message": "{{workflow.parameters.arg-1}}",
            },
        )

Something like wt.get_argument("arg-1") would be better.

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Addressing this issue would also be a good time to consolidate the get_parameter[s_as] functions that are duplicated (except for "steps." vs "tasks." in obj.value assignment this was a bug addressed in #624) in Step and Task

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We've also had feedback that knowing whether to use value or value_from can be confusing (e.g. you could do value="{{inputs.parameters.my-value}} or (I think) value_from=ValueFrom(expression="inputs.parameters.my-value") - maybe we can figure out a way to assign to one of these automatically based on the input? Both of these are still using Argo expressions though.

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Tasks:

• Get artifacts in native Hera - fixed in Add support for templatable exit handlers and V4 examples #613
• Get workflow arguments in native Hera - fixed in Add support for templatable exit handlers and V4 examples #613
• Consolidate get_parameter functions from Step and Task
• Proposal for value/value_from improvements (in a new issue)

Examples to update:

• script_argument_passing.py
• global_parameters.py