Add index_type tsdb support to OpenSearch sink for Prometheus metrics

[srikanthpadakanti]

Description

Add index_type: tsdb support to the OpenSearch sink for writing Prometheus metrics to OpenSearch TSDB indices. The sink converts Data Prepper Metric events (Gauge, Sum, Histogram, Summary) into TSDB's {labels, timestamp, value} document format, expanding complex types (histograms into per-bucket documents, summaries into per-quantile documents) so no intermediate processor is needed.

Issues Resolved

#6644
Resolves #6644

Check List

• [ X ] New functionality includes testing.
• New functionality has a documentation issue. Please link to it in this PR.
  • New functionality has javadoc added
• [ X ] Commits are signed with a real name per the DCO

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[github-actions]

✅ License Header Check Passed

All newly added files have proper license headers. Great work! 🎉

[srikanthpadakanti]

@dlvenable @kkondaka Could you please trigger the remaining workflows and review this?

[dlvenable]

Thank you @srikanthpadakanti for this contribution!

[dlvenable]

Thank you @srikanthpadakanti for this contribution!

[dlvenable]

@kkondaka , Could you take a review of this as you have worked quite a bit with Prometheus?

[kkondaka]

Looks like some of this code is similar to what is in the Prometheus sink. Should we move this code to some common library?

[srikanthpadakanti]

The sanitization logic here serves a different purpose. PrometheusTimeSeries sanitizes for Prometheus remote write naming conventions (unit suffixes, OpenMetrics rules), while TSDBDocumentBuilder sanitizes for the TSDB space-delimited keyword format (spaces to underscores, key prefix rules).

The methods share a similar name but the actual logic does not overlap. Extracting to a common library would couple two different output format requirements.

[dlvenable]

@srikanthpadakanti , On this topic, does Prometheus have any Java libraries that might have similar logic?

[srikanthpadakanti]

@dlvenable Checked PrometheusNaming in prometheus-metrics-model. It validates and escapes names for Prometheus exposition formats but does not do the kind of transformation we need. Their sanitizeLabelName only strips leading double-underscore prefixes, it does not replace invalid characters. They have no equivalent for replacing spaces in values (our TSDB delimiter requirement) or building sorted key-value label strings. The methods solve different problems at different layers.