experimental: Add System Resource instead of $resources url

[kof]

Description

ref #3308

TODO:

• - Remove copy for curl

Steps for reproduction

Add Variable, System Resource, open Select, check texts

Code Review

• hi @kof, 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