Add video classification pipeline (#20151)

* 🚧 wip video classification pipeline

* 🚧 wip - add is_decord_available check

* 🐛 add missing import

* ✅ add tests

* 🔧 add decord to setup extras

* 🚧 add is_decord_available

* ✨ add video-classification pipeline

* 📝 add video classification pipe to docs

* 🐛 add missing VideoClassificationPipeline import

* 📌 add decord install in test runner

* ✅ fix url inputs to video-classification pipeline

* ✨ updates from review

* 📝 add video cls pipeline to docs

* 📝 add docstring

* 🔥 remove unused import

* 🔥 remove some code

* 📝 docfix

src/transformers/testing_utils.py

@@ -51,6 +51,7 @@ from .utils import (
     is_apex_available,
     is_bitsandbytes_available,
     is_bs4_available,
+    is_decord_available,
     is_detectron2_available,
     is_faiss_available,
     is_flax_available,
@@ -446,6 +447,13 @@ def require_spacy(test_case):
     return unittest.skipUnless(is_spacy_available(), "test requires spacy")(test_case)
 
 
+def require_decord(test_case):
+    """
+    Decorator marking a test that requires decord. These tests are skipped when decord isn't installed.
+    """
+    return unittest.skipUnless(is_decord_available(), "test requires decord")(test_case)
+
+
 def require_torch_multi_gpu(test_case):
     """
     Decorator marking a test that requires a multi-GPU setup (in PyTorch). These tests are skipped on a machine without