add prefix and fix example

docs/widgets/services/customapi.md

@@ -103,7 +103,7 @@ mappings:
 
 ## Data Transformation
 
-You can manipulate data with the following tools `remap`, `scale` and `suffix`, for example:
+You can manipulate data with the following tools `remap`, `scale`, `prefix` and `suffix`, for example:
 
 ```yaml
 - field: key4
@@ -120,7 +120,11 @@ You can manipulate data with the following tools `remap`, `scale` and `suffix`,
   label: Power
   format: float
   scale: 0.001 # can be number or string e.g. 1/16
-  suffix: kW
+  suffix: "kW"
+- field: key6
+  label: Price
+  format: float
+  suffix: "$"
 ```
 
 ## List View

src/widgets/customapi/component.jsx

@@ -90,6 +90,12 @@ function formatValue(t, transformation, rawValue) {
     // nothing
   }
 
+  // Apply fixed prefix.
+  const prefix = transformation?.prefix;
+  if (prefix) {
+    value = `${prefix} ${value}`;
+  }
+
   // Apply fixed suffix.
   const suffix = transformation?.suffix;
   if (suffix) {