CloudMonitoring: Initial GCM Schema (#67739)

* Initial GCM schema work

- Split types for convenience
- Update conditionals where needed
- Update type references

* Add additional supporting types

* Add some more accessory and legacy types

* Add missing type

* Rename backend folder

* Add missing generated file

* Review

pkg/tsdb/cloud-monitoring/preprocessor.go

@@ -0,0 +1,22 @@
+package cloudmonitoring
+
+type preprocessorType int
+
+const (
+	PreprocessorTypeNone preprocessorType = iota
+	PreprocessorTypeRate
+	PreprocessorTypeDelta
+)
+
+func toPreprocessorType(preprocessorTypeString string) preprocessorType {
+	switch preprocessorTypeString {
+	case "none":
+		return PreprocessorTypeNone
+	case "rate":
+		return PreprocessorTypeRate
+	case "delta":
+		return PreprocessorTypeDelta
+	default:
+		return PreprocessorTypeNone
+	}
+}