Creating Java 17 version of CloudStorage sample with Gemini

[Mukamik]

This PR creates a Java 17 version of the Cloud Storage sample.
The sample was created with Gemini during a livestream, and contains a change to the test to use @ExtendsWith and MockitoExtension instead of the existing Mock approach for StorageOptions..

[snippet-bot]

Here is the summary of changes.

You are about to add 3 region tags.

• flexible/java-17/cloudstorage/pom.xml:44, tag gae_flex_storage_dependencies
• flexible/java-17/cloudstorage/src/main/appengine/app.yaml:15, tag gae_flex_cloudstorage_yaml
• flexible/java-17/cloudstorage/src/main/java/com/example/cloudstorage/UploadServlet.java:35, tag gae_flex_storage_app

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