CloudWatch: fix custom namespace for listing dimension keys, refactor to non-pointer types, add test assertions, rename packages (#59106)

Co-authored-by: Erik Sundell <erik.sundell87@gmail.com>

pkg/tsdb/cloudwatch/models/resources/resource_request.go

@@ -0,0 +1,22 @@
+package resources
+
+import (
+	"fmt"
+	"net/url"
+)
+
+type ResourceRequest struct {
+	Region string
+}
+
+func getResourceRequest(parameters url.Values) (*ResourceRequest, error) {
+	request := &ResourceRequest{
+		Region: parameters.Get("region"),
+	}
+
+	if request.Region == "" {
+		return nil, fmt.Errorf("region is required")
+	}
+
+	return request, nil
+}