FSE Beta: Change homepage setting in the Site editor (latest posts or front page)

### What

The homepage setting is an important one for overall site design, but it's not available in the Site editor.

This is tracked in Core, but there hasn't been any recent progress: https://github.com/WordPress/gutenberg/issues/28341

Whether in Core or in WP.com, we need this setting to be prominent. So users can choose what they want on the most important page of their site. It repeatedly came up in Cylon's empathy exercises, where users would be dropped into the Site editor on the Index template and start editing it as if it were a single page.

Related, maybe choosing posts or front page for this setting could be part of an in editor Gutenboarding step to configure the site.

The issue identifies the Site editor and links Gutenberg issue 28341 as the existing Core tracking item, but it names no files, tests, or entry points. Start by reviewing that linked issue and the Site editor implementation; done means users can prominently choose latest posts or a front page from the editor.

Written by the indexing model from the issue text.