Add: Template and template_lock to post types endpoint.

[jorgefilipecosta]

Trac: https://core.trac.wordpress.org/ticket/61477

Backports WordPress/gutenberg#62488 into the core.
Adds template and template_lock property of the post type to post types REST API endpoint.

This change allows to fix a bug where the template of a page is not respected when creating a new page on the site editor.

The update on the unit test is in progress and is still missing.

Testing

With the Gutenberg plugin disabled.
I added the following test code to a PHP file:

function myplugin_register_template() {
    $post_type_object = get_post_type_object( 'page' );
    $post_type_object->template = array(
        array( 'core/image' ),
    );
	$post_type_object->template_lock = 'all';
}
add_action( 'init', 'myplugin_register_template' );

I opened the site editor and pasted:
wp.data.select('core').getPostType( 'page' );

I verified the template and template_lock information was included.
I repeated the test with the Gutenberg plugin enabled to make sure things worked well together.

[github-actions]

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