Fix link in Pipeline documentation

[junhl]

What does this PR do?

Fix link in few following Pipeline documentations, as originally reported by #28224

• https://huggingface.co/docs/transformers/en/main_classes/pipelines#transformers.Conversation
• https://huggingface.co/docs/transformers/en/main_classes/pipelines#transformers.TextGenerationPipeline
• https://huggingface.co/docs/transformers/en/main_classes/pipelines#transformers.Text2TextGenerationPipeline

Fixes #28224
Consulted comments in previous PR attempts in #28231 and #30562

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Documentation: @stevhliu and @MKhalusova

[junhl]

Currently checks seem to be failing from original main, not from changes in this PR. Will rebase once main is fixed.

Review can be done @stevhliu @gante

EDIT: checks are now all green

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[stevhliu]

Looks good, thanks for the fix! 🤗