Refactor Datasets API docs for easier navigation: [Ray Datasets API](https://ray--27592.org.readthedocs.build/en/27592/data/api/api.html)
### Changes
1. Create a new Datasets API base page.
2. Split existing APIs into separate pages.
3. Split `Dataset` and `DatasetPipeline` methods into separate sections.
1. Used `autosummary` to generate overview tables at the top of each of these pages. Open to other suggestions e.g. moving the summary to the top of each section instead.
2. **Note:** Every time we add a new method we need to explicitly add it here as well.
4. Add Input/Output APIs.
1. I chose to split these primarily by data format rather than type, since it's easier to navigate, and the existing [Creating Datasets](https://docs.ray.io/en/master/data/creating-datasets.html) User Guide already does the latter.
6. Add `Block` and `DataBatch` (should we add these aliases?)
7. Remove existing `package-ref`.
Continuing docs overhaul, tune now has:
- [x] better landing page
- [x] a getting started guide
- [x] user guide was cut down, partially merged with FAQ, and partially integrated with tutorials
- [x] the new user guide contains guides to tune features and practical integrations
- [x] we rewrote some of the feature guides for clarity
- [x] we got rid of sphinx-gallery for this sub-project (only data and core left), as it looks bad and is unnecessarily complicated anyway (plus, makes the build slower)
- [x] sphinx-gallery examples are now moved to markdown notebook, as started in #22030.
- [x] Examples are tested in the new framework, of course.
There's still a lot one can do, but this is already getting too large. Will follow up with more fine-tuning next week.
Co-authored-by: Antoni Baum <antoni.baum@protonmail.com>
Co-authored-by: Kai Fricke <krfricke@users.noreply.github.com>
This PR consolidates both #21667 and #21759 (look there for features), but improves on them in the following way:
- [x] we reverted renaming of existing projects `tune`, `rllib`, `train`, `cluster`, `serve`, `raysgd` and `data` so that links won't break. I think my consolidation efforts with the `ray-` prefix were a little overeager in that regard. It's better like this. Only the creation of `ray-core` was a necessity, and some files moved into the `rllib` folder, so that should be relatively benign.
- [x] Additionally, we added Algolia `docsearch`, screenshot below. This is _much_ better than our current search. Caveat: there's a sphinx dependency that needs to be replaced (`sphinx-tabs`) by another, newer one (`sphinx-panels`), as the former prevents loading of the `algolia.js` library. Will follow-up in the next PR (hoping this one doesn't get re-re-re-re-reverted).
