Elasticsearch integration: missing index_stats alias on index mappings

[klacabane]

The index_stats property is used to query the indices from the index documents to power the SM elasticsearch Indices tab. We're currently missing an alias definition on that property in the elasticsearch integration package which causes the code path to return empty results[1].

Note that running a similar query in the dev tools will return a 400 error which appears to be swallowed in our code. We should investigate if there's any reason behind that and consider returning an erroneous status code instead.

{
  "error" : {
    "root_cause" : [
      {
        "type" : "illegal_argument_exception",
        "reason" : "no mapping found for index_stats.index in order to collapse on"
      }
    ],
  ....
  "status" : 400
}

AC

• indices tab loads corresponding documents from the index stream
• (optional) API endpoint returns an erroneous http response when mandatory mapping is not defined

[1]

[elasticmachine]

Pinging @elastic/infra-monitoring-ui (Team:Infra Monitoring UI)

[matschaffer]

Would @neptunian 's work to try to get us to metrics-* (#119112) also fix this issue maybe?

[klacabane]

I think Integrations-related issues are out of this PR scope, so tracking this separately

[klacabane]

Fixed in elastic/integrations#3928