UI: Show values set in `templateDefaults`

# Summary

It would be nice if values that are set in the `templateDefaults` are also shown in the UI. Take the following example:

```yaml
apiVersion: argoproj.io/v1alpha1
kind: Workflow
metadata:
generateName: hello-world-
spec:
entrypoint: whalesay
templateDefaults:
container:
env:
- name: TEST_VARIABLE
value: "hi"
templates:
- name: whalesay
container:
image: docker/whalesay:latest
command: [bash]
args: ["-c", "echo $TEST_VARIABLE"]
```

The container is given the `TEST_VARIABLE` by default, but the UI is showing there are no ENV variables for this container:


It would be nice if the variable set in the defaults also shows up there.

# Use Cases

We use the `templateDefaults` regularly in our workflows to set env variables. It would be more clear if these env variables also show up in the UI.

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**Message from the maintainers**:

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Start by locating the UI view that displays a container's environment variables, then read how it gets those values from a workflow. Compare the displayed variables with the example's `templateDefaults.container.env`; done means the `TEST_VARIABLE` default appears in the UI for the `whalesay` container.

Written by the indexing model from the issue text.