Update exit list signing infra for contract based exits #2122

Job	Run time
check	18s
clippy	37s
test	2m 23s
rustfmt	5s
audit	8s
integration-test-althea-payment	9m 50s
integration-test-db-migration	6m 32s
integration-test-debts	8m 52s
integration-test-eth-payments	12m 0s
integration-test-five-nodes	9m 5s
integration-test-multi-exit	9m 47s
integration-test-validate-contract	6m 42s
cross-armv7	1m 11s
cross-aarch64	1m 15s
	1h 8m 45s

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