Add way to do local dev offline for site

[Snugug]

Description

Currently, you need to have Sanity API access to contribute to site. This is not ideal for open source development.

Suggested solution

Whenever there's a build, also provide an archive of the most recent pull from Sanity and make it available, maybe as a release, and add a codepath to allows https://github.com/chromeos/chromeos.dev/blob/main/site/lib/sanity.ts to switch to use that archive instead.

Alternative

No response

Additional context

No response

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Check that there isn't already an issue that requests the same feature to avoid creating a duplicate.
• Make sure this is a ChromeOS.dev (the ChromeOS documentation and news site) issue and not a general ChromeOS issue. If you're looking to request a feature for ChromeOS, please report a ChromeOS problem or send feedback instead.
• Check that this is a concrete feature request. For Q&A, either ask in the Chromebook Help Community or join the #chromeos or #chromeos-forum channels in the Google Developer Community Discord.

### Tasks
- [x] Create archive of Sanity data dump
- [ ] Create an archive of images when a flag is passed into the build
- [ ] Redirect images to local copy on `dev:offline`
- [ ] Make content and image archive available in a release people can download