spqr-coordinator use pretty log by default

[Denchick]

Describe the bug
If you do not specify pretty_log field in your config and do not pass prettyLog flag to the CLI, then spqr-coordinator will use pretty log by default.

To Reproduce

➜  spqr git:(roles-v2) ./spqr-coordinator --config ./examples/coordinator.yaml --qdb-impl etcd
2025/03/10 15:32:27 Running config: {
  "log_level": "info",
  "qdb_addr": "localhost:2379",
  "coordinator_port": "7002",
  "grpc_api_port": "7003",
  "host": "localhost",
  "auth": null,
  "frontend_tls": null,
  "shard_data": "examples/shard_data.yaml",
  "use_systemd_notifier": false,
  "systemd_notifier_debug": false,
  "iteration_timeout": 0
}
3:32PM INF running coordinator app
3:32PM ERR qdb already taken, waiting for connection error="qdb is already in use."

Expected behavior
spqr-coordinator should use structured json log by default.