Client deprecation notice should be written in JSON when --json option is used

[jpraynaud]

Why

When the --json option is used in the client the deprecation notice is not formatted in JSON:

$ mithril-client --aggregator-endpoint https://aggregator.testing-sanchonet.api.mithril.network/aggregator snapshot download latest --genesis-verification-key $(curl https://raw.githubusercontent.com/input-output-hk/mithril/main/mithril-infra/configuration/testing-sanchonet/genesis.vkey) --json
`snapshot` command is deprecated, use `cardano-db` instead
{"timestamp": "2024-04-03T10:39:05.815084733+00:00", "step_num": 1, "total_steps": 5, "message": "Checking local disk info…"}
{"timestamp": "2024-04-03T10:39:05.815358611+00:00", "step_num": 2, "total_steps": 5, "message": "Fetching the certificate and verifying the certificate chain…"}

What

Format the deprecation notice in JSON when the --json option is used:

{"warning": "`snapshot` command is deprecated, use `cardano-db` instead", "type": "deprecation"}

How

• Handle the JSON formatted warning when --json option is used