Fix --log-format example to conform to glog format

[genkami]

According to GKE's fluent-bit config, logs should be of the format ^(?<severity>\w)(?<time>\d{4} [^\s]*)\s+(?<pid>\d+)\s+(?<source_file>[^ \]]+)\:(?<source_line>\d+)\]\s(?<message>.*)$. (I found it by running kubectl describe cm fluentbit-gke-config-v1.0.6 -n kube-system on my GKE cluster.)

The example in doc lacks \:(?<source_line>\d+) part, so I added it.

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[repokitteh-read-only]

Hi @genkami, welcome and thank you for your contribution.

We will try to review your Pull Request as quickly as possible.

In the meantime, please take a look at the contribution guidelines if you have not done so already.

🐱

Caused by: #18808 was opened by genkami.

see: more, trace.

[snowp]

This seems fine to me, have you verified that the output is as expected?

[genkami]

Yes. I deployed my Envoy with this cmd flag and saw that the logs are parsed correctly like this:

{
  "jsonPayload": {
    "message": "[1][main]initializing epoch 0 (base id=0, hot restart version=11.104)",
    "pid": "1"
  },
  "severity": "INFO",
  "sourceLocation": {
    "file": "envoy/source/server/server.cc",
    "line": "330"
  },
  ...
}

[snowp]

Thanks!