Warn on duplicate service BOM refs during BOM processing

[Zureno]

Description

Adds a warning log for duplicate service BOM references during BOM ingestion.

The method distinctComponentsByIdentity(...) already logs a warning when duplicate BOM references are encountered for components. However, the equivalent logic in distinctServicesByIdentity(...) silently ignored duplicate BOM references for services.

This change aligns the behavior of service processing with component processing by logging a warning when multiple services share the same BOM reference.

This improves diagnostics when ingesting malformed or incorrectly generated SBOMs and helps operators identify issues with SBOM generators.

Addressed Issue

No existing issue.
Improves consistency and observability in BOM processing.

Additional Details

During BOM ingestion, BomUploadProcessingTask deduplicates both components and services using their identity and BOM reference.

For components, the method distinctComponentsByIdentity(...) already detects and logs a warning when multiple components share the same BOM reference:

final boolean isBomRefUnique = identitiesByBomRef.putIfAbsent(component.getBomRef(), componentIdentity) == null;
if (!isBomRefUnique) {
    LOGGER.warn("...");
}

### Checklist

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- [x] I have read and understand the [contributing guidelines](../CONTRIBUTING.md#pull-requests)
- [ ] This PR fixes a defect, and I have provided tests to verify that the fix is effective
- [x] This PR implements an enhancement, and I have provided tests to verify that it works as intended
- [~] This PR introduces changes to the database model, and I have added corresponding [update logic](https://github.com/DependencyTrack/dependency-track/tree/master/src/main/java/org/dependencytrack/upgrade)
- [~] This PR introduces new or alters existing behavior, and I have updated the [documentation](https://github.com/DependencyTrack/dependency-track/tree/master/docs/_docs) accordingly

[owasp-dt-bot]

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