chore: update project id constants (#358)

## Summary

Add extra constants for LD attribute extraction.

## How did you test this change?

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<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Constant-only changes; main risk is downstream integrations depending
on the old `X-LaunchDarkly-Project` header casing or different attribute
names.
> 
> **Overview**
> Updates Go OTEL constants to better support LaunchDarkly project
identification: normalizes `LDProjectIDHeader` to lowercase
(`x-launchdarkly-project`) and adds a new `LDProjectIDAttribute`
(`launchdarkly.project_id`) alongside the existing Highlight attribute.
> 
> Reintroduces explicit *deprecated* constants for legacy
Highlight/session/trace/source keys (`highlight_project_id`,
`highlight_session_id`, `highlight_trace_id`, `Source`) while keeping
the canonical `highlight.*` attributes unchanged, enabling
backward-compatible extraction paths.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
498330e. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: Vadman97

sdk/highlight-go/otel.go

@@ -34,16 +34,22 @@ const OTLPDefaultEndpoint = "https://otel.highlight.io:4318"
 
 const ErrorURLAttribute = "URL"
 
+const LDProjectIDHeader = "x-launchdarkly-project"
 const ProjectIDHeader = "x-highlight-project"
-const LDProjectIDHeader = "X-LaunchDarkly-Project"
-const DeprecatedProjectIDAttribute = "highlight_project_id"
-const DeprecatedSessionIDAttribute = "highlight_session_id"
-const DeprecatedRequestIDAttribute = "highlight_trace_id"
-const DeprecatedSourceAttribute = "Source"
+
+const LDProjectIDAttribute = "launchdarkly.project_id"
 const ProjectIDAttribute = "highlight.project_id"
+const DeprecatedProjectIDAttribute = "highlight_project_id"
+
 const SessionIDAttribute = "highlight.session_id"
+const DeprecatedSessionIDAttribute = "highlight_session_id"
+
 const RequestIDAttribute = "highlight.trace_id"
+const DeprecatedRequestIDAttribute = "highlight_trace_id"
+
 const SourceAttribute = "highlight.source"
+const DeprecatedSourceAttribute = "Source"
+
 const TraceTypeAttribute = "highlight.type"
 const TraceKeyAttribute = "highlight.key"
 const EnvironmentAttribute = "environment"