Add `fast-runtime` feature to chain-spec-generator #991

Job	Run time
Extract integration tests from matrix	3s
Extract runtimes from matrix	3s
build-chain-spec-generator	23m 44s
integration-test (asset-hub-kusama, asset-hub-kusama-integration-tests)	43m 7s
integration-test (asset-hub-polkadot, asset-hub-polkadot-integration-tests)	43m 12s
runtime-test (polkadot, polkadot-runtime, relay/polkadot, wss://polkadot-try-runtime-node.parity-...	20m 36s
runtime-test (kusama, staging-kusama-runtime, relay/kusama, wss://kusama-try-runtime-node.parity-...	20m 31s
runtime-test (glutton-kusama, glutton-kusama-runtime, system-parachains/gluttons/glutton-kusama, ...	23m 45s
runtime-test (asset-hub-kusama, asset-hub-kusama-runtime, system-parachains/asset-hubs/asset-hub-...	22m 26s
runtime-test (asset-hub-polkadot, asset-hub-polkadot-runtime, system-parachains/asset-hubs/asset-...	21m 53s
runtime-test (bridge-hub-kusama, bridge-hub-kusama-runtime, system-parachains/bridge-hubs/bridge-...	21m 39s
runtime-test (bridge-hub-polkadot, bridge-hub-polkadot-runtime, system-parachains/bridge-hubs/bri...	21m 23s
runtime-test (collectives-polkadot, collectives-polkadot-runtime, system-parachains/collectives/c...	20m 38s
runtime-test (encointer-kusama, encointer-kusama-runtime, system-parachains/encointer, wss://kusa...	21m 8s
	5h 4m 8s

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