RUM-1836 feat(otel-tracer): support multi level tags using key flattening

[ganeshnj]

What and why?

Currently, attributes that are array or set which is composition of primitive types are not supported.

How?

Attributes are flattened using the recursive flattening.

This is inspired from Java version of tracer https://github.com/DataDog/dd-trace-java/blob/0f986a71765d0bad85ed4e5c3bc6ef44b8cb78fe/dd-java-agent/instrumentation/opentelemetry/opentelemetry-1.4/src/main/java/datadog/trace/instrumentation/opentelemetry14/trace/OtelSpan.java#L51-L63

The idea here is to create a key along with the path and save the value as it is in a flat dictionary (tags). In case of arrays, items are indexed with key.{index} pattern.

Review checklist

• Feature or bugfix MUST have appropriate tests (unit, integration)
• Make sure each commit and the PR mention the Issue number or JIRA reference
• Add CHANGELOG entry for user facing changes

Custom CI job configuration (optional)

• Run unit tests for Core, RUM, Trace, Logs, CR and WVT
• Run unit tests for Session Replay
• Run integration tests
• Run smoke tests
• Run tests for tools/

[ncreated]

Looks fine and its super clear 👌. I'm thinking why such significant change to the format of tags didn't require update in any tests added earlier - perhaps we could be missing integration coverage, no?

What would you say for adding an integration-unit test for this concept (from setting some tags to seeing them in encoded event)?

[ganeshnj]

Looks fine and its super clear 👌. I'm thinking why such significant change to the format of tags didn't require update in any tests added earlier - perhaps we could be missing integration coverage, no?

What would you say for adding an integration-unit test for this concept (from setting some tags to seeing them in encoded event)?

That's because we are not working with internal of DatadogTracer, we know [String: String] works perfect and well tested.

Currently not needed, but when we start to deprecated OTTracer, yes then we need to migrate those test cases.