Update exit list signing infra for contract based exits #2120

Job	Run time
check	24s
clippy	37s
integration-test-althea-payment	9m 1s
integration-test-debts	8m 22s
rustfmt	6s
audit	12s
integration-test-eth-payments	10m 53s
integration-test-five-nodes	8m 4s
integration-test-multi-exit	9m 46s
integration-test-validate-contract	6m 9s
integration-test-db-migration	6m 39s
test	3m 10s
cross-aarch64	1m 22s
cross-armv7	2m 30s
	1h 7m 15s

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