[BUG] EventName is ignored in the OTel logs source

Describe the bug
The latest OTel log spec has included the EventName in the protocol buffer definition (https://github.com/open-telemetry/opentelemetry-proto/blob/v1.9.0/opentelemetry/proto/logs/v1/logs.proto).

However, the OTel logs source of data prepper does not include this field. When we put the data with the EventName, the EventName will be ignored and will not show in the output.

To Reproduce
Steps to reproduce the behavior:

1. Create ingestion pipeline with OTel source and any destination
2. Put the follow testing data to the pipeline endpoint.

awscurl --service osis \
  -X POST \
  "{pipeline_endpoint}/logs" \
  -H 'Content-Type: application/json' \
  -d '{
    "resourceLogs": [{
      "scopeLogs": [{
        "logRecords": [{
          "timeUnixNano": "1739999999000000000",
          "severityText": "ERROR",
          "eventName": "payment.gateway.timeout",
          "body": {
            "stringValue": "Test with EventName field"
          },
          "attributes": [{
            "key": "transaction.id",
            "value": {
              "stringValue": "txn-67890"
            }
          }]
        }]
      }]
    }]
  }'

3. Verify the data in the destination

Expected behavior
The EventName field should be shown in the destination

Screenshots
If applicable, add screenshots to help explain your problem.

Environment (please complete the following information):

• OS: [e.g. Ubuntu 20.04 LTS]
• Version [e.g. 22]

Additional context
The issue should stem from the following code.
https://github.com/opensearch-project/data-prepper/blob/main/data-prepper-plugins/otel-proto-common/src/main/java/org/opensearch/dataprepper/plugins/otel/codec/OTelProtoOpensearchCodec.java#L298-L327