Docs: separate generate section
# What does this PR do?

A conclusion of the latest doc brainstorming section with @patrickvonplaten was that generate-related doc discoverability will become harder as we add more guides. The plan would envision a tutorial page and a few new developer guides -- in addition to the existing task pages, developer guide, and API reference.

As such, we converged on the need for a new doc section, under which most new docs will reside (see #24575 for the plan), with a focus on the first L of LLMs.

There is no section that would fit perfectly, this is (IMO) the best compromise: it contains a bit of "task", "developer guide", and "performance and scalability", but "task" is the most obvious place to look for this information 🤗 
_The documentation is not available anymore as the PR was closed or merged._