fix: add backwards compatibility for children in code text

[kof]

Description

Initially we allowed using any component inside code text and now we need to keep backwards compatibility because its not easy to migrate that to pure text.

Steps for reproduction

1. would need to find any old instance with code text that has other instances inside
2. see that it still works
3. override it with new code property

Code Review

• hi @istarkov , I need you to do
  • conceptual review (architecture, feature-correctness)
  • detailed review (read every line)
  • test it on preview

Before requesting a review

• made a self-review
• added inline comments where things may be not obvious (the "why", not "what")

Before merging

• tested locally and on preview environment (preview dev login: 5de6)
• updated test cases document
• added tests
• if any new env variables are added, added them to .env.example and the builder/env-check.js if mandatory