feat(host_metrics source): Add process virtual memory metric

[nionata]

Summary

Add virtual memory metric to the process host metrics collector. The current metric only covers process RSS.

Change Type

• Bug fix
• New feature
• Non-functional (chore, refactoring, docs)
• Performance

Is this a breaking change?

• Yes
• No

How did you test this PR?

make environment CONTAINER_TOOL="podman"

mkdir /etc/vector && cat << EOF > /etc/vector/vector.yaml
sources:
  in:
    type: "host_metrics"
    collectors:
      - "process"

sinks:
  out:
    inputs:
      - "in"
    type: "console"
    encoding: 
      codec: "native_json"
EOF

cargo run | jq .
...
{
  "metric": {
    "name": "process_memory_virtual_usage",
    "namespace": "host",
    "tags": {
      "collector": "process",
      "command": "target/debug/vector",
      "host": "...",
      "name": "vector-worker",
      "pid": "74413"
    },
    "timestamp": "2025-01-11T01:14:11.300421047Z",
    "kind": "absolute",
    "gauge": {
      "value": 836136960
    }
  }
}

Does this PR include user facing changes?

• Yes. Please add a changelog fragment based on our guidelines.
• No. A maintainer will apply the "no-changelog" label to this PR.

Checklist

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References