move opentelemetry into trace package, and refactoring (#996)

* move opentelemetry into trace package, and refactoring

* rename rewritten package names

core/trace/opentelemetry/config.go

@@ -0,0 +1,12 @@
+package opentelemetry
+
+// TraceName represents the tracing name.
+const TraceName = "go-zero"
+
+// A Config is a opentelemetry config.
+type Config struct {
+	Name     string  `json:",optional"`
+	Endpoint string  `json:",optional"`
+	Sampler  float64 `json:",default=1.0"`
+	Batcher  string  `json:",default=jaeger"`
+}