Update observability-with-otel.md (#36302)

Require the following package to add HTTP instrumentation:

```xml
<PackageReference Include="OpenTelemetry.Instrumentation.Http" Version="1.5.0-beta.1" />
```

Author: alyiox

docs/core/diagnostics/observability-with-otel.md

@@ -123,6 +123,7 @@ Use the NuGet Package Manager or command line to add the following NuGet package
    <PackageReference Include="OpenTelemetry.Exporter.Zipkin" Version="1.5.0" />
    <PackageReference Include="OpenTelemetry.Extensions.Hosting" Version="1.5.0" />
    <PackageReference Include="OpenTelemetry.Instrumentation.AspNetCore" Version="1.5.0-beta.1" />
+   <PackageReference Include="OpenTelemetry.Instrumentation.Http" Version="1.5.0-beta.1" />
 </ItemGroup>
 ```