Bug 1862536 - Add a Nimbus variable for Firefox Suggestion types.

This commit adds:

* An `awesomebar-suggestion-provider` Nimbus feature to a new
  component-specific manifest in the `feature-fxsuggest` component.
* An `available-suggestion-types` variable for that feature, which
  holds a map of all available suggestion types that the
  `FxSuggestSuggestionProvider` can return.

This lets us toggle suggestion types remotely as part of our
experiments.

app/nimbus.fml.yaml

@@ -141,6 +141,15 @@ import:
           download-button: true,
           open-in-app-button: true
         }
+  - path: ../../android-components/components/feature/fxsuggest/fxsuggest.fml.yaml
+    channel: release
+    features:
+      awesomebar-suggestion-provider:
+        - value:
+            available-suggestion-types: {
+              "amp": true,
+              "wikipedia": true,
+            }
 
 features:
   toolbar: