/cmd: Improved devx of benching many pallets simultaneously (#6007)

### Improved devx of running many pallets simultaneously

Changes to /cmd:
- Replace (flip) `--continue-on-fail` with `--fail-fast`, but only for
`bench`. This makes all pallets/runtimes run non-stop by default, as it
was primary use-case during tests
- The list of successful/failed pallets was hard to find within tons of
logs, so decided to write only needed logs in a file, and output as a
summary in the workflow and in the comment
- Side fix: updated `tasks_example` to `pallet_example_tasks` to make
compliant with standard naming

<img width="1006" alt="image"
src="https://github.com/user-attachments/assets/14896041-7018-4a0d-92b7-4508e81913c2">

+ added command results to workflow summary:
<img width="1275" alt="image"
src="https://github.com/user-attachments/assets/b4a8afdb-dc9f-4ff9-9720-28a88956035f">

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Co-authored-by: GitHub Action <action@github.com>