An option to set a limit to the number of transactions generated by the
`load` command of the e2e framework.

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---

#### PR checklist

- [ ] Tests written/updated
- [x] Changelog entry added in `.changelog` (we use
[unclog](https://github.com/informalsystems/unclog) to manage our
changelog)
- [ ] Updated relevant documentation (`docs/` or `spec/`) and code
comments

(cherry picked from commit 6722f33)