[enhancement] Add new metrics based on repo format

[andrey-gava]

Hello!

It would be great to add some new metrics, which can show usage of repos by they format(type)

All this data resides in data url json, in key "gauge" and have next names:
nexus.analytics.format_request_rates count (lables format,type,status)
nexus.analytics.repository_asset_count_by_format_type count (lables format,type)
nexus.analytics.repository_component_count_by_format_type count (lables format,type)
nexus.analytics.repository_type_counts count (lables format,type)

All this keys have similar structure.
Like:

{
  "gauges": {
    "nexus.analytics.format_request_rates": {
      "value": [
        {
          "key": "value",
          "key": "value",
          "key": "value",
        },
   ......
        {
          "key": "value",
          "key": "value",
          "key": "value",
        },
      ]
    },
 },
}

So maybe it take only one parse script to write, and then duplicate it for every new metric key.

Example from my server:

"nexus.analytics.repository_type_counts": { "value": [ { "format": "npm", "type": "hosted", "count": 1 }, { "format": "docker", "type": "hosted", "count": 4 }, { "format": "maven2", "type": "proxy", "count": 2 }, { "format": "maven2", "type": "hosted", "count": 3 }, { "format": "yum", "type": "hosted", "count": 3 }, { "format": "maven2", "type": "group", "count": 1 }, { "format": "nuget", "type": "proxy", "count": 1 }, { "format": "yum", "type": "group", "count": 1 }, { "format": "nuget", "type": "group", "count": 1 }, { "format": "yum", "type": "proxy", "count": 4 }, { "format": "npm", "type": "proxy", "count": 1 }, { "format": "helm", "type": "hosted", "count": 1 }, { "format": "nuget", "type": "hosted", "count": 1 } ] },