fix: correctly parse and render total metric values and labels (not just last label) in kof UI

[AndrejsPon00]

This PR fixes an issue where metrics with multiple labels were not parsed and rendered correctly. The UI previously receive and used a single (last) label value instead of aggregating and exposing all labels and values. The Prometheus parser, backend response format, and UI rendering were updated so metrics now include distinct label entries and a value.

Examples Prometheus metric input:

vl_data_size_bytes{type="indexdb"} 199695
vl_data_size_bytes{type="storage"} 125139890

Before (incorrect) metrics were parsed into a single numeric value:

"vl_data_size_bytes": 125139890

After (correct) backend now returns separated labels and values:

{
  "vl_data_size_bytes": [
    {
      "labels": { "type": "indexdb" },
      "value": 199695
    },
    {
      "labels": { "type": "storage" },
      "value": 125139890
    }
  ]
}