The toBSON call can fail if the doc is larger than 16MB. User can create arbitrarily large docs in their pipeline, so we should handle this case. In this case we should send a DLQ message instead of failing the processor (we do the same thing for failures to write a doc in $merge or $emit).

        case HttpClient::HttpMethod::kPATCH: {
            rawDoc = tojson(payloadDoc.toBson(), mongo::JsonStringFormat::ExtendedRelaxedV2_0_0);
            headers.emplace_back("Content-Type: application/json");
            break;