fix: Correctly log Exceptions

[nielm]

Adds bunyan Error serializer (to log {err:err} correctly with stack trace etc. Fix log messages to include error message in log message

Before: exception stack traces were not included in logging:

err=new Error('myerror');
logger.error({err:err, message:`Failed`});
{
  "timestamp": {
    "seconds": 1712143463,
    "nanos": 476000070
  },
  "severity": "ERROR",
  "logging.googleapis.com/insertId": "..........5RSfIdnw_0SuufwA49eSIJ",
  "name": "redis-cluster-autoscaler",
  "hostname": "dastardly.c.googlers.com",
  "pid": 208009,
  "level": 50,
  "err": {},
  "message": "Failed",
  "msg": "myerror",
  "time": "2024-04-03T11:24:23.476Z",
  "v": 0,
  "logName": "projects/redis-autoscaler/logs/redis-cluster-autoscaler"
}

After, includes err object correctly with stack trace

err=new Error('myerror');
logger.error({err:err, message:Failed: ${err}});
{
  "timestamp": {
    "seconds": 1712143548,
    "nanos": 480999946
  },
  "severity": "ERROR",
  "logging.googleapis.com/insertId": "..........E5w78.D4S4fuorMiE2SJ3e",
  "name": "redis-cluster-autoscaler",
  "hostname": "dastardly.c.googlers.com",
  "pid": 208429,
  "level": 50,
  "err": {
    "message": "myerror",
    "name": "Error",
    "stack": "Error: myerror\n    at REPL3:1:5\n    at Script.runInThisContext (node:vm:122:12)\n    at REPLServer.defaultEval (node:repl:594:29)\n    at bound (node:domain:433:15)\n    at REPLServer.runBound [as eval] (node:domain:444:12)\n    at REPLServer.onLine (node:repl:924:10)\n    at REPLServer.emit (node:events:529:35)\n    at REPLServer.emit (node:domain:489:12)\n    at [_onLine] [as _onLine] (node:internal/readline/interface:423:12)\n    at [_line] [as _line] (node:internal/readline/interface:894:18)"
  },
  "message": "Failed: Error: myerror",
  "msg": "myerror",
  "time": "2024-04-03T11:25:48.481Z",
  "v": 0,
  "logName": "projects/redis-autoscaler/logs/redis-cluster-autoscaler"
}