Support for resource injection (#3383)

Co-authored-by: Kevin Wan <wanjunfeng@gmail.com>

core/trace/resource.go

@@ -0,0 +1,10 @@
+package trace
+
+import "go.opentelemetry.io/otel/attribute"
+
+var attrResources = make([]attribute.KeyValue, 0)
+
+// AddResources add more resources in addition to configured trace name.
+func AddResources(attrs ...attribute.KeyValue) {
+	attrResources = append(attrResources, attrs...)
+}