Add speed metrics to all example scripts + template
# What does this PR do?

This does the same as #9198 but on all examples scripts and the example template.
The eval metrics are already reported with the other metrics, so need to add anything for them. Not sure about the refactor since this shouldn't really be a function in transformers (nothing to do with transformers models) so we would have to define it in every one of those scripts, which kind of takes the same length.<|||||>re: eval/train - except n_objs is missing from metrics - remember we had to add it separately in `finetune_trainer` when you refactored it?

re: refactor: I haven't suggested anything for the core - we have utils.py for that.<|||||>Yes, but this is something I just did in `finetune_trainer` to have it output the same things as before, for other scripts I don't want that reported several times (it's already logged at the beginning of training/evaluation).