Additional layout parameters are passed in incorrectly

Problem/Motivation

Due to changes in 📌 Convert Layout plugin discovery to attributes Active additional parameters are not passed in layout definition correctly (rocketship_core.layouts.yml).
Now it's additional[additional][region_type].

Proposed resolution

Make region_type attribute of layout definition.

Before

rs_footer:
  additional:
    region_type: footer

After

rs_footer:
  region_type: footer