[Security Solution][Detection Engine] Errors from rule querying are not being populated in the UI

[FrankHassanabad]

Kibana version:
7.9.0

Describe the bug:
If you happen to have a bug with a query anywhere, then Elastic Search returns documents but sometimes also returns both documents and errors and other times just errors with no results. At the moment the detection engine does not show the errors.

This is due to code around the lines here:
https://github.com/elastic/kibana/blob/master/x-pack/plugins/security_solution/server/lib/detection_engine/signals/single_search_after.ts#L62

It will figure out when an exception is thrown and report that as an error but you have situations where you have partial results or no results and one or more errors.

Steps to reproduce:
Go to a detections rule and add an invalid value within the exceptions such as this one below:

Notice that rsa.internal.level value is not a numeric but a text string.

Now, if you open up the single_search_after.ts and add this line of code:

    console.log('****** SEARCH RESULT *****', JSON.stringify(nextSearchAfterResult, null, 2));
    return { searchResult: nextSearchAfterResult, searchDuration: makeFloatString(end - start) };

You will begin seeing errors in addition to the queries being returned. However, you don't get any errors showing up in the UI for the rule its self. The rule still looks like it is functioning completely correctly when in reality it does have errors that require users to fix within exceptions.

Errors, but you also get result hits back as well.

****** SEARCH RESULT ***** {
  "took": 1120,
  "timed_out": false,
  "_shards": {
    "total": 21,
    "successful": 20,
    "skipped": 12,
    "failed": 1,
    "failures": [
      {
        "shard": 0,
        "index": "filebeat-8.0.0-2020.09.02-000001",
        "node": "UmFIfD_iQfepBl6sUyEk2g",
        "reason": {
          "type": "query_shard_exception",
          "reason": "failed to create query: For input string: \"blah\"",
          "index_uuid": "F5LVi0LMTOa72Ma0otsXMA",
          "index": "filebeat-8.0.0-2020.09.02-000001",
          "caused_by": {
            "type": "number_format_exception",
            "reason": "For input string: \"blah\""
          }
        }
      }
    ]

Expected behavior:
At the very least we should bubble up the errors even if we decide to create the signals themselves.

[elasticmachine]

Pinging @elastic/siem (Team:SIEM)