feat(integrations): Land initial Nimbus FML

- We're trying to integrate with Nimbus and unblock SRE

- Lands the initial yaml

Closes: FXA-9124

configs/nimbus.yaml

@@ -0,0 +1,22 @@
+about:
+  description: Nimbus Feature Manifest for Accounts Web testing
+channels:
+  - production
+features:
+  example-feature:
+    description: An example feature
+    variables:
+      enabled:
+        description: If the feature is enabled
+        type: Boolean
+        default: false
+      something:
+        description: Another variable
+        type: Option<String>
+        default: null
+    defaults:
+      - channel: production
+        value: { "something": "wicked" }
+types:
+  objects: {}
+  enums: {}