Add video classification pipeline (#20151)
* :construction: wip video classification pipeline
* :construction: wip - add is_decord_available check
* :bug: add missing import
* :white_check_mark: add tests
* :wrench: add decord to setup extras
* :construction: add is_decord_available
* :sparkles: add video-classification pipeline
* :memo: add video classification pipe to docs
* :bug: add missing VideoClassificationPipeline import
* :pushpin: add decord install in test runner
* :white_check_mark: fix url inputs to video-classification pipeline
* :sparkles: updates from review
* :memo: add video cls pipeline to docs
* :memo: add docstring
* :fire: remove unused import
* :fire: remove some code
* :memo: docfix