docs: add extract field to execRecipe docs (#553)

## Description:
Part of #503

## Is this change user facing?
YES

## References (if applicable):
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docs/docs/starlark-reference/exec-recipe.md

@@ -12,6 +12,20 @@ exec_recipe = ExecRecipe(
     # Each item corresponds to one shell argument, so ["echo", "Hello world"] behaves as if you ran "echo 'Hello World'" in the shell.
     # MANDATORY
     command = ["echo", "Hello, World"],
+
+    # The extract dictionary can be used for filtering specific parts of a response
+    # assigning that output to a key-value pair, where the key is the reference 
+    # variable and the value is the specific output. 
+    # 
+    # Specifcally: the key is the way you refer to the extraction later on and
+    # the value is a 'jq' string that contains logic to extract parts from response 
+    # body that you get from the exec_recipe used
+    # 
+    # To lean more about jq, please visit https://devdocs.io/jq/
+    # OPTIONAL (DEFAULT:{})
+    extract = {
+        "extractfield" : ".name.id",
+    },
 )
 ```