Introduce a REST API endpoint for sites

[jeremyfelt]

It should be possible to manage sites in a multisite configuration through the REST API.

• List sites: GET wp/v2/sites/
• Retrieve a site: GET wp/v2/sites/<id>
• Create a site: POST wp/v2/sites/
• Update a site: PUT wp/v2/sites/<id>
• Delete a site: DELETE wp/v2/sites/<id>

Data included in a site object should at least mirror the data available for the site in wp_blogs. Additional ideal pieces of data for a site include blogname, blogdescription, home, and siteurl. It's possible that creating a new meta table for sites can help developers register meta for inclusion with a site object (See #37923).

Sites should be accessible by default for authenticated users only. Network (global) admins should have access to all sites. Site users should have access to the sites they are members of. The "My Sites" list is a great candidate for exploring how this will work. See #15317.

As of the introduction of get_sites() in 4.6.0, retrieving sites is a much better experience. The methods used to create, update, and delete sites in multisite are not as pleasant right now. We should investigate each of these and determine what can be done to streamline the process. The first improvement is probably in creating a site. See #40364.

[flixos90]

These tickets belong to our planned roadmap (a few of them not per final decision), so flagging with a keyword for better overview.

[flixos90]

For reference: Once #37923 and #38025 are finished, an additional part of this ticket will also be to implement a site meta endpoint.

[spacedmonkey]

First pass at patch. 40365.diff

It uses wpmu_create_blog, wpmu_delete_blog and update_blog_details for now, as other crud functions are not available.

[joehoyle]

This looks like a good start! I wonder if we could perhaps add this to a github PR on the existing repo) and do feedback there, as doing so on a patch this size is really no fund!

​https://github.com/WP-API/wp-api-site-endpoints is the repo, on the PR it might be to write down why / if this is different than what exists there already.