Add `node` name to generated spans

# Summary

The new tracing functionality for workflows is really nice 🚀 it would be even more useful if one could tell from a node span which template it executed (and, prospectively, also with which parameters etc.).

## Use Cases

- Investigating traces for workflows

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**Message from the maintainers**:

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No file or test is named in the issue. Start by locating the workflow tracing implementation that creates node spans and inspect how the node name and executed template are represented; done means generated node spans expose the node name for workflow trace investigation.

Written by the indexing model from the issue text.