[BUG] Service-map relationship should be created regardless of missing traceGroupName

[chenqi0805]

Describe the bug
The service-map-relationship are skipped when traceGroupName is null:

https://github.com/opensearch-project/data-prepper/blob/main/data-prepper-plugins/service-map-stateful/src/main/java/org/opensearch/dataprepper/plugins/processor/ServiceMapStatefulProcessor.java#L245

To Reproduce
Steps to reproduce the behavior:

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

Expected behavior
We should still create the relationship regardless of traceGroupName missing

Screenshots
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Environment (please complete the following information):

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

Additional context
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