refactor: Reduce OTel dependencies

The `OpenFeature.Contrib.Hooks.Otel` project currently references
(1) an exporter implementation which libraries should _not_ do
under any normal circumstances, and (2) the main OpenTelemetry
project which is excessive given all of the excellent work by
the dotnet/runtime and open-telemetry/opentelemetry-dotnet teams
have done over the last couple of years to ensure that the BCL
types in `System.Diagnostics` conform to OTel standards.

This commit removes (1) and pares down (2) to from `OpenTelemetry`
to `OpenTelemetry.Api` to shrink the dependency footprint we ship
to consumers.

At this point, I would argue that this hooks package should meet
the minimal dependency requirement for upstream inclusion in the
main OpenFeature package, but deferring that discussion for now.

Signed-off-by: Austin Drenski <austin@austindrenski.io>

src/OpenFeature.Contrib.Hooks.Otel/OpenFeature.Contrib.Hooks.Otel.csproj

@@ -13,8 +13,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="OpenTelemetry" Version="1.4.0" />
-    <PackageReference Include="OpenTelemetry.Exporter.Console" Version="1.4.0" />
+    <PackageReference Include="OpenTelemetry.Api" Version="1.4.0" />
   </ItemGroup>
 
 </Project>

src/OpenFeature.Contrib.Hooks.Otel/TracingHook.cs

@@ -1,6 +1,7 @@
 using OpenFeature.Model;
 using System.Threading.Tasks;
 using System.Collections.Generic;
+using System.Diagnostics;
 using OpenTelemetry.Trace;
 
 namespace OpenFeature.Contrib.Hooks.Otel
@@ -22,17 +23,16 @@ public class TracingHook : Hook
         public override Task After<T>(HookContext<T> context, FlagEvaluationDetails<T> details,
             IReadOnlyDictionary<string, object> hints = null)
         {
-            var span = Tracer.CurrentSpan;
-            if (span != null)
-            {
-                var attributes = new Dictionary<string, object>
+            Activity.Current?
+                .SetTag("feature_flag.key", details.FlagKey)
+                .SetTag("feature_flag.variant", details.Variant)
+                .SetTag("feature_flag.provider_name", context.ProviderMetadata.Name)
+                .AddEvent(new ActivityEvent("feature_flag", tags: new ActivityTagsCollection
                 {
-                    {"feature_flag.key", details.FlagKey},
-                    {"feature_flag.variant", details.Variant},
-                    {"feature_flag.provider_name", context.ProviderMetadata.Name}
-                };
-                span.AddEvent("feature_flag", new SpanAttributes(attributes));
-            }
+                    ["feature_flag.key"] = details.FlagKey,
+                    ["feature_flag.variant"] = details.Variant,
+                    ["feature_flag.provider_name"] = context.ProviderMetadata.Name
+                }));
 
             return Task.CompletedTask;
         }
@@ -47,11 +47,7 @@ public override Task After<T>(HookContext<T> context, FlagEvaluationDetails<T> d
         public override Task Error<T>(HookContext<T> context, System.Exception error,
             IReadOnlyDictionary<string, object> hints = null)
         {
-            var span = Tracer.CurrentSpan;
-            if (span != null)
-            {
-                span.RecordException(error);
-            }
+            Activity.Current?.RecordException(error);
 
             return Task.CompletedTask;
         }