MM-21898: Part 2. Add opentracing (#13904)

* initial implementation of opentracing

* app layer

* Revert Makefile

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* cleanup

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* [ci]

* autogenerate interface

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* missed vendor files

* updated interfaces

* updated store layers

* lint fixes

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* finishing layer generators and nested spans

* added errors and b3 support

* code review

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* fixed build error due to misplased flag.Parse()

* code review addressed

Makefile

@@ -200,8 +200,10 @@ endif
 endif
 
 app-layers: ## Extract interface from App struct
-	env GO111MODULE=off $(GO) get -u github.com/reflog/struct2interface
-	$(GOBIN)/struct2interface -f "app" -o "app/app_iface.go" -p "app" -s "App" -i "AppIface" -t ./app/layer_generators/app_iface.go.tmpl
+    # The following commented commands can be used to re-generate the AppIface from the App struct
+	# env GO111MODULE=off $(GO) get gopkg.in/reflog/struct2interface.v0
+	# $(GOBIN)/struct2interface.v0 -f "app" -o "app/app_iface.go" -p "app" -s "App" -i "AppIface" -t ./app/layer_generators/app_iface.go.tmpl
+	$(GO) run ./app/layer_generators -in ./app/app_iface.go -out ./app/opentracing_layer.go -template ./app/layer_generators/opentracing_layer.go.tmpl
 
 i18n-extract: ## Extract strings for translation from the source code
 	env GO111MODULE=off $(GO) get -u github.com/mattermost/mattermost-utilities/mmgotool