tsp-openapi3: import examples

### Clear and concise description of the problem

Now that #2700 is complete, the `tsp-openapi` tool should be updatet to do the reverse and add example(s) to the TypeSpec. (A single opExample/example if using `example`, multiple if using `examples`.)

### Checklist

- [X] Follow our [Code of Conduct](https://github.com/microsoft/typespec/blob/main/CODE_OF_CONDUCT.md)
- [X] Read the [docs](https://typespec.io/docs/).
- [X] Check that there isn't already an issue that request the same feature to avoid creating a duplicate.