Update example with a full dart project

Update example with a full dart project that includes references to nitric.

Author: chimon2000

example/.gitignore

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+# https://dart.dev/guides/libraries/private-files
+# Created by `dart pub`
+.dart_tool/

example/README.md

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+A server app built using [Nitric](nitric.io) with an entrypoint in `bin/`, library code
+in `lib/`, and example unit test in `test/`.
+
+# Running the sample
+
+## Running with the Dart SDK
+
+You can run the example with the [Dart SDK](https://dart.dev/get-dart)
+like this:
+
+```
+$ dart run bin/example.dart
+```

example/analysis_options.yaml

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+include: package:lints/recommended.yaml

example/pubspec.yaml

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+name: example
+description: A sample command-line application.
+version: 1.0.0
+publish_to: none
+
+environment:
+  sdk: ^3.2.5
+
+dependencies:
+  nitric_sdk:
+    path: ../
+  uuid: ^4.3.3
+
+dev_dependencies:
+  lints: ^2.1.0
+  test: ^1.24.0