Add athena ref page (#5961)

## What are you changing in this pull request and why?

Adding the Amazon Athena /ref page
Additionally organized the adapter ref page sidebar in alphabetical
order

## Checklist
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- [ ] Add versioning components, as described in [Versioning
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- [ ] Add a note to the prerelease version [Migration
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- [ ] Review the [Content style
guide](https://github.com/dbt-labs/docs.getdbt.com/blob/current/contributing/content-style-guide.md)
so my content adheres to these guidelines.
- [ ] For [docs
versioning](https://github.com/dbt-labs/docs.getdbt.com/blob/current/contributing/single-sourcing-content.md#about-versioning),
review how to [version a whole
page](https://github.com/dbt-labs/docs.getdbt.com/blob/current/contributing/single-sourcing-content.md#adding-a-new-version)
and [version a block of
content](https://github.com/dbt-labs/docs.getdbt.com/blob/current/contributing/single-sourcing-content.md#versioning-blocks-of-content).
- [ ] Add a checklist item for anything that needs to happen before this
PR is merged, such as "needs technical review" or "change base branch."

Adding or removing pages (delete if not applicable):
- [ ] Add/remove page in `website/sidebars.js`
- [ ] Provide a unique filename for new pages
- [ ] Add an entry for deleted pages in `website/vercel.json`
- [ ] Run link testing locally with `npm run build` to update the links
that point to deleted pages

---------

Co-authored-by: Ly Nguyen <[email protected]>
Co-authored-by: Amy Chen <[email protected]>