add constant to go sdk (#114)

## Summary

Context key const reported by some of the SDKs.

## How did you test this change?

NA

## Are there any deployment considerations?

no

Author: Vadman97

sdk/highlight-go/otel.go

@@ -68,6 +68,7 @@ const LDExceptionID = "launchdarkly.exception.id"
 const FeatureFlagScope = "feature_flag"
 const FeatureFlagSpanName = "evaluation"
 const FeatureFlagSpanEventName = FeatureFlagScope + "." + FeatureFlagSpanName
+const FeatureFlagContextId = "feature_flag.context.id"
 const FeatureFlagContextKey = "feature_flag.context.key"
 const FeatureFlagContextKeys = "feature_flag.contextKeys"
 const FeatureFlagSetID = "feature_flag.set.id"