Ability to set the heading level for OpenAPI blocks

[JaniceManwiller]

Whenever you add an OpenAPI block to a page, it always uses the same heading level - I assume it's heading 1. You cannot group the blocks under a heading - for example "Widget management functions", "Authentication functions". If you try to add headings, both the headings and the block labels just display as one list.

So essentially the only way to group the blocks is to use different topics.

It would be nice to be able to specify the heading level for a block, so that you can have meaningful groupings.