Add --log-format json

[rukai]

Adds a flag that sets shotover to write its tracing logs as json instead of the default human readable format.
e.g.

{"timestamp":"2022-12-01T04:13:17.880070Z","level":"INFO","fields":{"message":"Starting Shotover 0.1.7"},"target":"shotover_proxy::runner"}
{"timestamp":"2022-12-01T04:13:17.880153Z","level":"INFO","fields":{"configuration":"Config { main_log_level: \"warn,shotover_proxy=warn\", observability_interface: \"0.0.0.0:9001\" }"},"target":"shotover_proxy::runner"}
{"timestamp":"2022-12-01T04:13:17.880182Z","level":"INFO","fields":{"topology":"Topology { sources: {\"cassandra_prod\": Cassandra(CassandraConfig { listen_addr: \"127.0.0.1:9042\", connection_limit: None, hard_connection_limit: None, tls: None, timeout: None })}, chain_config: {\"main_chain\": [DebugForceEncode(DebugForceEncodeConfig { encode_requests: true, encode_responses: true }), CassandraSinkSingle(CassandraSinkSingleConfig { address: \"127.0.0.1:9043\", tls: None, connect_timeout_ms: 3000, read_timeout: None })]}, source_to_chain_mapping: {\"cassandra_prod\": \"main_chain\"} }"},"target":"shotover_proxy::runner"}
{"timestamp":"2022-12-01T04:13:17.880403Z","level":"INFO","fields":{"message":"Loaded chains [\"main_chain\"]"},"target":"shotover_proxy::config::topology"}
{"timestamp":"2022-12-01T04:13:17.880469Z","level":"INFO","fields":{"message":"Starting Cassandra source on [127.0.0.1:9042]"},"target":"shotover_proxy::sources::cassandra_source"}
{"timestamp":"2022-12-01T04:13:17.880566Z","level":"INFO","fields":{"message":"Loaded sources [[\"cassandra_prod\"]] and linked to chains"},"target":"shotover_proxy::config::topology"}
{"timestamp":"2022-12-01T04:13:17.880634Z","level":"INFO","fields":{"message":"accepting inbound connections"},"target":"shotover_proxy::server"}
{"timestamp":"2022-12-01T04:13:17.981697Z","level":"INFO","fields":{"message":"Negotiating protocol version: rejecting version 66 (configure the client to use a supported version by default to improve connection time)"},"target":"shotover_proxy::codec::cassandra","span":{"id":2,"source":"CassandraSource","name":"connection"},"spans":[{"id":2,"source":"CassandraSource","name":"connection"}]}
{"timestamp":"2022-12-01T04:13:17.982215Z","level":"INFO","fields":{"message":"Negotiating protocol version: rejecting version 65 (configure the client to use a supported version by default to improve connection time)"},"target":"shotover_proxy::codec::cassandra","span":{"id":3,"source":"CassandraSource","name":"connection"},"spans":[{"id":3,"source":"CassandraSource","name":"connection"}]}
{"timestamp":"2022-12-01T04:13:19.396892Z","level":"INFO","fields":{"message":"Negotiating protocol version: rejecting version 66 (configure the client to use a supported version by default to improve connection time)"},"target":"shotover_proxy::codec::cassandra","span":{"id":7,"source":"CassandraSource","name":"connection"},"spans":[{"id":7,"source":"CassandraSource","name":"connection"}]}
{"timestamp":"2022-12-01T04:13:19.397418Z","level":"INFO","fields":{"message":"Negotiating protocol version: rejecting version 65 (configure the client to use a supported version by default to improve connection time)"},"target":"shotover_proxy::codec::cassandra","span":{"id":8,"source":"CassandraSource","name":"connection"},"spans":[{"id":8,"source":"CassandraSource","name":"connection"}]}
{"timestamp":"2022-12-01T04:13:19.446729Z","level":"INFO","fields":{"message":"Negotiating protocol version: rejecting version 66 (configure the client to use a supported version by default to improve connection time)"},"target":"shotover_proxy::codec::cassandra","span":{"id":12,"source":"CassandraSource","name":"connection"},"spans":[{"id":12,"source":"CassandraSource","name":"connection"}]}
{"timestamp":"2022-12-01T04:13:19.447337Z","level":"INFO","fields":{"message":"Negotiating protocol version: rejecting version 65 (configure the client to use a supported version by default to improve connection time)"},"target":"shotover_proxy::codec::cassandra","span":{"id":13,"source":"CassandraSource","name":"connection"},"spans":[{"id":13,"source":"CassandraSource","name":"connection"}]}
{"timestamp":"2022-12-01T04:13:19.503113Z","level":"WARN","fields":{"message":"Server-side warning: `USE <keyspace>` with prepared statements is considered to be an anti-pattern due to ambiguity in non-qualified table names. Please consider removing instances of `Session#setKeyspace(<keyspace>)`, `Session#execute(\"USE <keyspace>\")` and `cluster.newSession(<keyspace>)` from your code, and always use fully qualified table names (e.g. <keyspace>.<table>). Keyspace used: test_prepare_statements, statement keyspace: test_prepare_statements, statement id: 2418a6606d64ccd02a7805fc4416a352","log.target":"datastax::internal::core::Decoder::decode_warnings","log.module_path":"datastax::internal::core::Decoder::decode_warnings","log.file":"decoder.cpp","log.line":134},"target":"datastax::internal::core::Decoder::decode_warnings"}
{"timestamp":"2022-12-01T04:13:19.614296Z","level":"ERROR","fields":{"message":"UHO H H\nYEET"},"target":"lib::cassandra_int_tests"}
{"timestamp":"2022-12-01T04:13:19.615360Z","level":"INFO","fields":{"message":"source CassandraSource was shutdown"},"target":"shotover_proxy::server"}
{"timestamp":"2022-12-01T04:13:19.615503Z","level":"INFO","fields":{"message":"Shotover was shutdown cleanly."},"target":"shotover_proxy::runner"}

My original motivation of this change is to be able to make assertions on tracing logs in our integration tests.

However users will want to be able to process shotovers logs programmatically so this is an important feature for shotover in its own right.
As such it should be reviewed for that purpose, as a user exposed feature.

To test it out you can run:

• cargo run uses --log-format human by default
• cargo run --log-format json

Feel free to bikeshed arg naming.

Due to a currently poor API from tracing the reload handle type currently includes whether we are using json formatting or not.
So in order to handle it generically we need to wrap each case in an enum and then pass that into our web server.

[benbromhead]

I wouldn't get too hung up on the web log control stuff we have at the moment, it's largely an "interesting" feature. We can start to work on it's idiosyncrasies when we get some proper user feedback