DOCS-3398: Add data client code samples to flutter sdk (#337)

* Add data client code samples to flutter sdk

Author: sguequierre

dartdoc_options.yaml

@@ -4,12 +4,14 @@ dartdoc:
       markdown: doc/Components.md
     "Services":
       markdown: doc/Services.md
+    "App":
+      markdown: doc/App.md
     "Viam SDK":
       markdown: doc/ViamSDK.md
     "Common":
       markdown: doc/Common.md
     "Protobuf Definitions":
       markdown: doc/Protobuf.md
   categoryOrder:
-    ["Components", "Services", "Common", "Viam SDK", "Protobuf Definitions"]
+    ["Components", "Services", "App", "Common", "Viam SDK", "Protobuf Definitions"]
   nodoc: ["**/di/**", "**/domain/**"]