Use structs to convert JSON outputs in the test framework

[ljoss17]

Proposal

In Hermes test framework it is sometimes required to parse JSON output of CLIs. As suggested in this comment, https://github.com/informalsystems/hermes/pull/3694#discussion_r1395448432, the test framework should use struct that match the expected output and which derive Deserialize. This will allow converting the JSON output in the expected struct to have a cleaner test framework

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