Mitigate `next_etrago_id` collisions

[gnn]

Don't know whether there are any open issues which this PR solves, but it should help with next_etrago_id collisions by generating IDs randomly in a manner which is relatively unlikely to generate collisions.

Before merging into dev-branch, please make sure that

• [ ] the CHANGELOG.rst was updated.
• [x] new and adjusted code is formated using black and isort.
• [ ] the Dataset-version is updated when existing datasets are adjusted.
• [ ] the branch was merged into the continuous-integration/run-everything-over-the-weekend-branch.
• [ ] the workflow is running successful in test mode.
• [ ] the workflow is running successful in Everything mode.

None of the above has happened yet, but I'll do so before the PR gets merged. I'll also assign reviewers, but since it's better to assign individual reviewers to specific commits, I'll do that later, too.

[nesnoj]

@gnn You said last week it ran successfully in test mode? Does this PR contain the latest code? I'd like to give it a try for DE on a RLI instance, do you think it's mature enough?