Supported pipeline tasks update
The docstring of the `transformers.pipeline` listed only 16 supported tasks while `SUPPORTED_TASKS` contains 24 tasks. This PR adds the missing tasks to the docstrings so that the generated reference docs accurately list all of the supported tasks here - https://huggingface.co/docs/transformers/main/en/main_classes/pipelines#transformers.pipeline 


_The documentation is not available anymore as the PR was closed or merged._