Plugins: Refactoring: Implement plugin instrumentation as a middleware (#76011)

* Plugins: Refactor instrumentation as plugin client middleware

* Simplify repeated code

* Fix compilation error

* Add comments

* Moved status and endpoint consts to utils.go

* Fix wrong endpoint name in CheckHealth InstrumentationMiddleware

* Add tests

* Fix wrong endpoint value in instrumentPluginRequestSize

* removed todo

* PR review feedback: use MustRegister

* PR review feedback: move tracing middleware before instrumentation middleware

* PR review feedback: removed decommissioned check

* PR review feedback: extract prometheus metrics into separate variables

pkg/services/pluginsintegration/clientmiddleware/utils.go

@@ -4,6 +4,17 @@ import (
 	"github.com/grafana/grafana-plugin-sdk-go/backend"
 )
 
+const (
+	statusOK        = "ok"
+	statusError     = "error"
+	statusCancelled = "cancelled"
+
+	endpointCallResource   = "callResource"
+	endpointCheckHealth    = "checkHealth"
+	endpointCollectMetrics = "collectMetrics"
+	endpointQueryData      = "queryData"
+)
+
 type callResourceResponseSenderFunc func(res *backend.CallResourceResponse) error
 
 func (fn callResourceResponseSenderFunc) Send(res *backend.CallResourceResponse) error {