[Entity Analytics] Improve response body for asset criticality delete route

[hop-dev]

While doing the API docs I noticed the asset criticality delete route did not return a response body, and returned a very ugly 404 if you attempted to delete something which didnt exist...

{"message":"{\"_index\":\".asset-criticality.asset-criticality-default\",\"_id\":\"host.name:my_host\",\"_version\":1,\"result\":\"not_found\",\"_shards\":{\"total\":2,\"successful\":1,\"failed\":0},\"_seq_no\":0,\"_primary_term\":1}","full_error":"{\"name\":\"ResponseError\",\"message\":\"{\\\"_index\\\":\\\".asset-criticality.asset-criticality-default\\\",\\\"_id\\\":\\\"host.name:my_host\\\",\\\"_version\\\":1,\\\"result\\\":\\\"not_found\\\",\\\"_shards\\\":{\\\"total\\\":2,\\\"successful\\\":1,\\\"failed\\\":0},\\\"_seq_no\\\":0,\\\"_primary_term\\\":1}\"}","status_code":404}%

I have now made it so that we return a boolean for if the record was deleted or not (false if the record didnt exist) and we also return the record that was deleted if it was, e.g...

{
    "deleted": true,
    "record": {
        "id_field": "host.name",
        "id_value": "my_host",
        "criticality_level": "medium_impact",
        "@timestamp": "2024-08-05T09:42:11.240Z"
    }
}

And if the record didnt exist...

{
    "deleted": false,
}

[elasticmachine]

Pinging @elastic/security-entity-analytics (Team:Entity Analytics)

[tiansivive]

LGTM

[kibana-ci]

💛 Build succeeded, but was flaky

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• FTR Configs #8

Test Failures

• [job] [logs] FTR Configs #8 / machine learning - anomaly detection forecasts with single metric job displays job results

Metrics [docs]

✅ unchanged

To update your PR or re-run it, just comment with:
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cc @hop-dev