Fix create_group in generate_perf_testdata to return group_id

What does this MR do?

Fixes create_group in qa generate_perf_testdata script so it correctly returns group_id, which is then used by create_project to create the require project under the group.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation created/updated or follow-up review issue created
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