Add support for flow.json fork syntax (#2747)

* Add support for flow.json fork syntax

* relax type

Author: jribbink

.changeset/fork-network-support.md

@@ -0,0 +1,8 @@
+---
+"@onflow/config": minor
+"@onflow/fcl-core": minor
+"@onflow/react-core": minor
+---
+
+Add support for fork networks (mainnet-fork, testnet-fork) to enable testing against forked emulator with automatic contract alias inheritance from parent networks. Fork networks allow developers to run their dapps and E2E tests against a local emulator that mirrors mainnet or testnet state, while supporting contract-specific overrides.
+