Print execution time of each example test

[kundaMwiza]

What does this PR do?

Show execution times of example tests

Output format:

1930.67s call     tests/test_examples.py::QuestionAnsweringExampleTester::test_run_qa_deberta                                                                                                                                                                                                                                              
1600.59s call     tests/test_examples.py::MultipleChoiceExampleTester::test_run_swag_groupbert                                                                                                                                                                                                                                             
1569.01s call     tests/test_examples.py::SummarizationExampleTester::test_run_summarization_t5                                                                                                                                                                                                                                            
1444.00s call     tests/test_examples.py::SummarizationExampleTester::test_run_summarization_mt5   

Fixes # (issue)

Before submitting

• [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• [ ] Did you make sure to update the documentation with your changes?
• [ ] Did you write any new necessary tests?

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint.