[Cloud security] Fix runtime fields scripts - checking field exist

[kfirpeled]

Summary

This PR address to an issue we have with backward and forward compatibility

For a robust check of the existence of a field, and that it has a value we first need to use doc.containsKey and afterwards to check it is not empty using empty property: doc["field.path"].empty

Checklist

• Unit or functional tests were updated or added to match the most common scenarios

How to test this

I would recommend using first the Dev Tools to check the runtime fields is correct
For example, I run a query with aggs to see when things break and when not

List of edge cases I've checked:

• What happens when field's mapping doesn't exist
• What happens when field's mapping exist but there are documents without that field
• Checking happy flow
• Checking field that doesn't exist and doesn't have mappings

Here is the query

  GET /logs-cloud_security_posture.findings_latest-default/_search
  {
    "size": 10,
    "runtime_mappings": { 
      "asset_identifier": {
        "type": "keyword",
        "script": {
          "source": """
          emit(doc["rule.benchmark.posture_type"].empty ? "empty" : doc["rule.benchmark.posture_type"].value)
          """}
      }
    },
    "query": {
      "match": {
        "asset_identifier": "empty"
      }
    },
    "aggs": {
      "score_by_cluster_id": {
        "terms": {
          "field": "asset_identifier"
        }
      }
    }
  }

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: 8aa8fd4

Metrics [docs]

Module Count

Fewer modules leads to a faster build time

id	before	after	diff
cloudSecurityPosture	166	167	+1

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
cloudSecurityPosture	193.2KB	194.0KB	+815.0B

Unknown metric groups

ESLint disabled line counts

id	before	after	diff
enterpriseSearch	19	21	+2
securitySolution	398	401	+3
total			+5

Total ESLint disabled count

id	before	after	diff
enterpriseSearch	20	22	+2
securitySolution	478	481	+3
total			+5

History

• 💛 Build #125001 was flaky 56523e9
• 💔 Build #124993 failed 1232bd7

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

[CohenIdo]

I tested it locally: LGTM

[kibanamachine]

💚 All backports created successfully

Status	Branch	Result
✅	8.8

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