Use of tasks groups for workspace generators

[Tcharl]

Contributes a bit to #28235 by using tasks groups on workspace generators.
Next steps: use of template framework and workspace types to avoid generator being stateful

FYI, didn't modify any line of logic or object: just moved code into different functions (using the new APIs)

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[Tcharl]

Don't think the errors are due to the code modified: seems to be the node and npm package version downloaded by the frontend plugin