Add UI for Fetch phase in Search Profiler

[cjcenizal]

In https://github.com/elastic/elasticsearch/pull/77064, ES added support for profiling the fetch phase. We need to update Search Profiler to surface this information. Here's an example of the shape of this info:

        "fetch": {
          "type": "fetch",
          "description": "fetch",
          "time_in_nanos": 660555,
          "breakdown": {
            "next_reader": 7292,
            "next_reader_count": 1,
            "load_stored_fields": 299325,
            "load_stored_fields_count": 5
          },
          "debug": {
            "stored_fields": ["_id", "_routing", "_source"]
          },
          "children": [
            {
              "type": "source",
              "description": "load _source",
              "time_in_nanos": 20443,
              "breakdown": {
                "next_reader": 745,
                "next_reader_count": 1,
                "process": 19698,
                "process_count": 5
              },
              "debug": {
                "loaded_nested": 0,
                "fast_path": 5
              }
            }
          ]
        }

This entails adding a new tab and designing the UI to make this information accessible:

[elasticmachine]

Pinging @elastic/kibana-stack-management (Team:Stack Management)

[elasticmachine]

Pinging @elastic/kibana-management (Team:Kibana Management)