Create a config hash scheme for identifying deployments

[Siegrift]

Related to api3dao/signed-api#240

Originally, Airnode feed implemented a logic to create a config hash that is sent as heartbeat to verify the deployment used the correct config. This feature is nice also for Airseeker, so this feature should be implemented in commons and used in both places.

Note, that similarly to the heartbeat, the CloudFormation entrypoint uses a similar script to verify the config, but uses md5 instead of keccak256. Ideally, both would use the same hashing function.