Docs: Add docs around feature toggles config (#19162)

docs/sources/installation/configuration.md

@@ -702,6 +702,11 @@ is false. This settings was introduced in Grafana v6.0.
 
 
 Set to true if you want to test alpha plugins that are not yet ready for general usage.
 Set to true if you want to test alpha plugins that are not yet ready for general usage.
 
 
+## [feature_toggles]
+### enable
+
+Keys of alpha features to enable, separated by space. Available alpha features are: `transformations`
+
 <hr />
 <hr />
 
 
 # Removed options
 # Removed options