elastic scaling RFC 103 end-to-end test

[alindima]

Adds a new zombienet-sdk test which verifies that elastic scaling works correctly both with the MVP and the new RFC 103 implementation which sends the core selector as a UMP signal.

Also enables the V2 receipts node feature for testnet genesis config.

Part of #5049

[paritytech-workflow-stopper]

All GitHub workflows were cancelled due to failure one of the required jobs.
Failed workflow url: https://github.com/paritytech/polkadot-sdk/actions/runs/12297500276
Failed job name: test-doc

[paritytech-workflow-stopper]

All GitHub workflows were cancelled due to failure one of the required jobs.
Failed workflow url: https://github.com/paritytech/polkadot-sdk/actions/runs/12297500276
Failed job name: build-rustdoc