feat(js): allow naming generates

[marcelfolaron]

Implements #3378 custom span names for generate steps. New optional parameter called stepName can be set to define the step name displayed in traces. Will default to "generate" if stepName is not set.

Checklist (if applicable):

• PR title is following https://www.conventionalcommits.org/en/v1.0.0/
• Tested (manually, unit tested, etc.)
• Docs updated (updated docs or a docs bug required)

[marcelfolaron]

Missed to commit my change to rename the parameter name in the testapp to stepName. Should build now