add pivot example for starlark processor (#7976)

plugins/processors/starlark/README.md

@@ -153,6 +153,7 @@ Attempting to modify the global scope will fail with an error.
 - [rename](/plugins/processors/starlark/testdata/rename.star)
 - [scale](/plugins/processors/starlark/testdata/scale.star)
 - [number logic](/plugins/processors/starlark/testdata/number_logic.star)
+- [pivot](/plugins/processors/starlark/testdata/pivot.star)
 
 Open a [PR](https://github.com/influxdata/telegraf/compare) to add any other useful Starlark examples. 
 

plugins/processors/starlark/testdata/pivot.star

@@ -0,0 +1,17 @@
+'''
+Pivots a key's value to be the key for another key.
+In this example it pivots the value of key `sensor`
+to be the key of the value in key `value`
+
+Input: 
+temperature sensor=001A0,value=111.48
+
+Output: 
+temperature 001A0=111.48
+'''
+ 
+ def apply(metric):
+   metric.fields[str(metric.fields['sensor'])] = metric.fields['value']
+   metric.fields.pop('value',None)
+   metric.fields.pop('sensor',None)
+   return metric