[RFC] Add fold_node RFC

[kboyarinov]

Description

Add RFC document for new fold_node in the Flow Graph.

Fixes # - issue number(s) if exists

Type of change

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• [ ] bug fix - change that fixes an issue
• [ ] new feature - change that adds functionality
• [ ] tests - change in tests
• [ ] infrastructure - change in infrastructure and CI
• [ ] documentation - documentation update

Tests

• [ ] added - required for new features and some bug fixes
• [ ] not needed

Documentation

• [ ] updated in # - add PR number
• [ ] needs to be updated
• [ ] not needed

Breaks backward compatibility

• [ ] Yes
• [ ] No
• [ ] Unknown

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