Initialize nested component structures with data

[bglw]

Currently, the only component shorthand available is:

button: "bookshop:button" #or:
buttons: ["bookshop:button"]

In both of these instances, the object or array will be initialized in the CMS empty. We should provide something like the following:

button: "bookshop:button!" #or:
buttons: ["bookshop:button!", "bookshop:button!"]

Where components suffixed with ! are pre-populated when added to the CMS.

Bonus considerations:

• If the core CMS adds a non-nullable object structure type, how would that be represented here?
• If a user tries bookshop:structure:content_blocks!, how should that behave, and what could be implemented to achieve this?
  • A structure key could be supplied? (bookshop:structure:content_blocks:title!)
• Alternative syntaxes:
  • Five buttons: bookshop:button(5)
  • A content_blocks array with starter components added: bookshop:structure:content_blocks(title,paragraph,button)