feat: Add metadata statistics to registry api

[ntkathole]

What this PR does / why we need it:

This PR enrich /metrics/resource_counts with feature store inventory metadata.

Extended the existing GET /metrics/resource_counts endpoint to include feature store inventory metadata alongside the existing resource counts, giving users a single-call view of their feature store without querying the registry directly.

The response now includes (in addition to the existing backward-compatible counts):

featureServices - list of registered services with name and project
featureViews - list of feature views with name, project, type (featureView/onDemandFeatureView/streamFeatureView), and per-view feature count
projects - list of projects (with description in all-projects mode)
registryLastUpdated - registry last-updated timestamp

{
  "total": {
    "entities": 4,
    "dataSources": 3,
    "savedDatasets": 0,
    "features": 20,
    "featureViews": 8,
    "featureServices": 6
  },
  "perProject": {
    "multiproject1": {
      "entities": 2,
      "dataSources": 3,
      "savedDatasets": 0,
      "features": 10,
      "featureViews": 4,
      "featureServices": 3
    },
    "multiproject2": {
      "entities": 2,
      "dataSources": 0,
      "savedDatasets": 0,
      "features": 10,
      "featureViews": 4,
      "featureServices": 3
    }
  },
  "featureServices": [
    {
      "name": "driver_activity_v2",
      "project": "multiproject1"
    },
    {
      "name": "driver_activity_v1",
      "project": "multiproject1"
    },
    {
      "name": "driver_activity_v3",
      "project": "multiproject1"
    },
    {
      "name": "driver_activity_v3",
      "project": "multiproject2"
    },
    {
      "name": "driver_activity_v1",
      "project": "multiproject2"
    },
    {
      "name": "driver_activity_v2",
      "project": "multiproject2"
    }
  ],
  "featureViews": [
    {
      "name": "driver_hourly_stats_fresh",
      "project": "multiproject1",
      "type": "featureView",
      "featureCount": 3
    },
    {
      "name": "driver_hourly_stats",
      "project": "multiproject1",
      "type": "featureView",
      "featureCount": 3
    },
    {
      "name": "transformed_conv_rate_fresh",
      "project": "multiproject1",
      "type": "onDemandFeatureView",
      "featureCount": 2
    },
    {
      "name": "transformed_conv_rate",
      "project": "multiproject1",
      "type": "onDemandFeatureView",
      "featureCount": 2
    },
    {
      "name": "driver_hourly_stats",
      "project": "multiproject2",
      "type": "featureView",
      "featureCount": 3
    },
    {
      "name": "driver_hourly_stats_fresh",
      "project": "multiproject2",
      "type": "featureView",
      "featureCount": 3
    },
    {
      "name": "transformed_conv_rate",
      "project": "multiproject2",
      "type": "onDemandFeatureView",
      "featureCount": 2
    },
    {
      "name": "transformed_conv_rate_fresh",
      "project": "multiproject2",
      "type": "onDemandFeatureView",
      "featureCount": 2
    }
  ],
  "projects": [
    {
      "name": "multiproject1",
      "description": "A project for driver statistics"
    },
    {
      "name": "multiproject2",
      "description": "A project for driver statistics"
    }
  ],
  "registryLastUpdated": "2026-03-26T07:43:11.019554Z"
}

Which issue(s) this PR fixes:

Fixes #5921

Checks

• I've made sure the tests are passing.
• My commits are signed off (git commit -s)
• My PR title follows conventional commits format

Testing Strategy

• Unit tests
• Integration tests
• Manual tests
• Testing is not required for this change

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[franciscojavierarceo]

looking now, resource_counts probably isn't the most intuitive name for an API but too late now 🤷‍♂️