API to define a default template for the template mode #32752
Description
WordPress 5.8 will introduce a template mode in the post editor https://make.wordpress.org/core/2021/06/14/introducing-the-template-editor-in-wordpress-5-8/
That mode allows users to create block templates and assign them to posts and pages. A default starting template is used to repopulate newly created templates.
Ideally, themes should be able to define the content of the initial template. Let's try to provide an API to do so. This API should be able to scale to FSE themes as well.
The simplest solution might be to add a settings to the block_editor_settings_all filter as this can be provided in php and made translatable easily.
An alternative would be a file in the theme (convention) but since we don't want to add block-templates to themes yet, it seems premature for this option.