Fix include-what-you-use

Author: jgomezselles

examples/manual_propagation/main.cc

@@ -6,12 +6,14 @@
 #include <string>
 #include <utility>
 
+#include "opentelemetry/context/context.h"
 #include "opentelemetry/context/propagation/global_propagator.h"
 #include "opentelemetry/context/propagation/text_map_propagator.h"
 #include "opentelemetry/context/runtime_context.h"
 #include "opentelemetry/exporters/ostream/span_exporter_factory.h"
 #include "opentelemetry/nostd/shared_ptr.h"
 #include "opentelemetry/nostd/string_view.h"
+#include "opentelemetry/nostd/variant.h"
 #include "opentelemetry/sdk/resource/resource.h"
 #include "opentelemetry/sdk/trace/exporter.h"
 #include "opentelemetry/sdk/trace/processor.h"
@@ -23,6 +25,9 @@
 #include "opentelemetry/trace/propagation/http_trace_context.h"
 #include "opentelemetry/trace/provider.h"
 #include "opentelemetry/trace/span.h"
+#include "opentelemetry/trace/span_context.h"
+#include "opentelemetry/trace/span_metadata.h"
+#include "opentelemetry/trace/span_startoptions.h"
 #include "opentelemetry/trace/tracer.h"
 #include "opentelemetry/trace/tracer_provider.h"