Ly docs explorer public preview (#4283)

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

Update Explorer docs for public preview. Merging from private rep

- [x] Update the page "Explore dbt projects"
- [x] Create release note

## Checklist
- [x] Review the [Content style
guide](https://github.com/dbt-labs/docs.getdbt.com/blob/current/contributing/content-style-guide.md)
and [About
versioning](https://github.com/dbt-labs/docs.getdbt.com/blob/current/contributing/single-sourcing-content.md#adding-a-new-version)
so my content adheres to these guidelines.

Adding new pages (delete if not applicable):
- [x] ~~Add page to `website/sidebars.js`~~ automated since the new page
is a release note
- [x] Provide a unique filename for the new page