Define grid layout programmatically

Hey!

The layout block is so useful, thanks for your work on it!

As I tend to want to tightly control how clients can add content I'm curious if you've thought about being able to setup the layout grid programmatically via attributes? The use case would be to create a custom block that contains an inner block that has a template that only allows the layout grid at top level and then the content in each column can be customized by the client.

Effectively you'd be able to create advanced grids (preferably for each breakpoint) and the client can then add content in the grid how they please, but with the upside that the grid layout is preserved. Being able to lock layout changes (optionally disable offset/span) would be pretty cool too, so you have even more control of the layout.

Thoughts?