Reporting backend metrics

[abbashus]

Issue #, if available:

Description of changes:

• Add new API _opendistro/_reports/stats to collect usage metrics and action metrics
• Metrics details:
  count: request count in the last minute
  total: total request count since the server is up
  user_error: 4xx error status code in the last minute
  system_error: all other error status code in the last minute

Sample Response:

{
  "on_demand_from_definition": {
    "create": {
      "system_error": 0,
      "user_error": {
        "invalid_report_def_id": 0
      },
      "count": 0,
      "total": 0
    }
  },
  "report_instance": {
    "info": {
      "user_error": {
        "invalid_report_id": 0,
        "missing_report_instance": 0
      },
      "total": 0,
      "system_error": 0,
      "count": 0
    },
    "update": {
      "count": 0,
      "system_error": 0,
      "total": 0,
      "user_error": {
        "missing_report_instance": 0,
        "invalid_report_id": 0,
        "invalid_status": 0
      }
    },
    "list": {
      "user_error": {
        "invalid_from_index": 0
      },
      "total": 0,
      "count": 0,
      "system_error": 0
    }
  },
  "permission_user_error": 0,
  "request_total": 0,
  "report_definition": {
    "info": {
      "system_error": 0,
      "count": 0,
      "user_error": {
        "invalid_report_def_id": 0,
        "missing_report_def_details": 0
      },
      "total": 0
    },
    "delete": {
      "count": 0,
      "system_error": 0,
      "user_error": {
        "invalid_report_def_id": 0,
        "missing_report_def_details": 0
      },
      "total": 0
    },
    "update": {
      "user_error": {
        "invalid_report_def_id": 0,
        "invalid_report_definition": 0,
        "missing_report_def_details": 0
      },
      "count": 0,
      "system_error": 0,
      "total": 0
    },
    "create": {
      "system_error": 0,
      "user_error": 0,
      "count": 0,
      "total": 0
    },
    "list": {
      "system_error": 0,
      "count": 0,
      "total": 0,
      "user_error": {
        "invalid_from_index": 0
      }
    }
  },
  "on_demand": {
    "create": {
      "user_error": {
        "invalid_begin_time": 0,
        "invalid_status": 0,
        "invalid_end_time": 0
      },
      "system_error": 0,
      "total": 0,
      "count": 0
    }
  },
  "exception": {
    "illegal_state": 0,
    "illegal_argument": 0,
    "io": 0,
    "es_security": 0,
    "es_status": 0,
    "version_conflict_engine": 0,
    "invalid_index_name": 0,
    "index_not_found": 0,
    "internal_server_error": 0
  },
  "es_security_permission_error": 0,
  "failed_request_count_system_error": 0,
  "success_count": 0,
  "request_count": 0,
  "failed_request_count_user_error": 0
}

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[codecov]

Codecov Report

Merging #282 (b68ad64) into dev (45abee7) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##              dev     #282   +/-   ##
=======================================
  Coverage   74.94%   74.94%           
=======================================
  Files          32       32           
  Lines        1764     1764           
  Branches      342      342           
=======================================
  Hits         1322     1322           
  Misses        437      437           
  Partials        5        5           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 45abee7...b68ad64. Read the comment docs.

[davidcui1225]

LGTM - just some minor comments

[akbhatta]

Please add javadoc for the classes and public methods.