[Refactor] Splitting pipelines.py into its own module. (#9279)
* Splitting pipelines into its own module.
* Moving everything into base.py
* Moving FeatureExtractionPipeline into its own file.
* TextGenerationPipeline.
* TextClassifictionPipeline
* ZeroShot + get_framework import.
* FillMaskPipeline
* NerPipeline + TokenClassificationPipeline
* QuestionAnsweringPipeline
* TableQuestionAnsweringPipeline
* ConversationnalPipeline
* Text2TextGenerationPipeline, TranslationPipeline, SummarizationPipeline
* Typo import fix.
* Relative imports.