Cloudwatch: Refactor dimension keys resource request (#57148)

* use new layered architecture in get dimension keys request

* go lint fixes

* pr feedback

* more pr feedback

* remove not used code

* refactor route middleware

* change signature

* add integration tests for the dimension keys route

* use request suffix instead of query

* use typed args also in frontend

* remove unused import

* harmonize naming

* fix merge conflict

pkg/tsdb/cloudwatch/models/http_error.go

@@ -0,0 +1,22 @@
+package models
+
+import "fmt"
+
+type HttpError struct {
+	Message    string
+	Error      string
+	StatusCode int
+}
+
+func NewHttpError(message string, statusCode int, err error) *HttpError {
+	httpError := &HttpError{
+		Message:    message,
+		StatusCode: statusCode,
+	}
+	if err != nil {
+		httpError.Error = err.Error()
+		httpError.Message = fmt.Sprintf("%s: %s", message, err)
+	}
+
+	return httpError
+}