Flexible Layout Templates - Add hero ROW by default to new templates

Description of the need When you create a flexible layout template and enable it for the default front page, there is no good place for the current hero block. You can create a hero row by changing the 'Row Width Behavior' to 'Always full width of page."

But this is not obvious and requires specific knowledge.

This issue came up here: https://github.com/backdrop/backdrop-issues/issues/4066

Proposed solution To add a default 'hero' row to each new flexible layout template. This would be a 4th row in addition to the current default 'header', 'content,' and 'footer' rows.

Proposed: * Header Row * Hero Row * Content Row * Footer Row

NOTE: I am not convinced that this is necessary, but would like to hear from others.

Alternatives that have been considered

I think an alternative would be to simply make it easier for a site builder to figure out how to make their own hero row. This MIGHT be sufficient. https://github.com/backdrop/backdrop-issues/issues/4081