templateDefaults validations are too strict

[gmeshkov]

Pre-bug-report checklist

1. This bug can be reproduced using pure Argo YAML

• Yes 👉 Please report a bug to the Argo Workflows GitHub 👈
• No

If yes, it is more likely to be an Argo bug unrelated to Hera. Please double check before submitting an issue to Hera.

2. I have searched for existing issues

• Yes

3. This bug occurs in Hera when...

• exporting to YAML
• submitting to Argo
• running on Argo with the Hera runner
• other: parsing workflow from JSON downloaded from an Argo cluster

Bug report

Describe the bug
A clear and concise description of what the bug is:
In Hera, template_defaults field is typed as an optional[Template]

hera/src/hera/workflows/models/io/argoproj/workflow/v1alpha1.py

Lines 4440 to 4441 in fed792c

	template_defaults: Annotated[
	Optional[Template],

However, as per Argo Workflows documentation, it is just a collection of overrides, not a full template. So if you download a workflow from a cluster where it was complimented with templateDefaults, pydantic in Hera fails the validations, expecting a full Template where e.g. something like this can be present:

    templateDefaults:
      inputs: {}
      outputs: {}
      metadata: {}
      container:
        name: ''
        env:
          - name: ARGO_INSTALLATION
            value: us-east2
        resources: {}
      script:
        name: ''
        env:
          - name: ARGO_INSTALLATION
            value: us-east2
        resources: {}
        source: ''

Error log if applicable:

   File ".../my_project/argo/util/api.py", line 120, in _get_graph_json_rest
    return Workflow.parse_obj(result.json())
   File ".../pydantic/x86_64_linux/lib/python3.12/site-packages/pydantic/v1/main.py", line 526, in parse_obj
    return cls(**obj)
           ^^^^^^^^^^
  File ".../pydantic/x86_64_linux/lib/python3.12/site-packages/pydantic/v1/main.py", line 341, in __init__
    raise validation_error
pydantic.v1.error_wrappers.ValidationError: 2 validation errors for Workflow
status -> storedWorkflowTemplateSpec -> templateDefaults -> container -> image
  field required (type=value_error.missing)
status -> storedWorkflowTemplateSpec -> templateDefaults -> script -> image
  field required (type=value_error.missing)```

**To Reproduce**
Full Hera code to reproduce the bug:
```py
# Not applicable, as requires templateDefaults being set up on the cluster

Expected behavior
Workflow is parsed all right.

Environment

• Hera Version: 5.14.3
• Python Version: 3.12
• Argo Version: 3.5.10