feat: Java SDK Api Key authorization sample

[ldetmer]

Description

Java Cloud SDK introduced a new API to allow users to authenticate via an API key. This provides a sample usage of the new setApiKey function.

Checklist

• [X] I have followed Sample Format Guide
• [X] pom.xml parent set to latest shared-configuration
• [X] Appropriate changes to README are included in PR
• [ ] These samples need a new API enabled in testing projects to pass (let us know which ones)
• [ ] These samples need a new/updated env vars in testing projects set to pass (let us know which ones)
• [X] Tests pass: mvn clean verify required
• [X] Lint passes: mvn -P lint checkstyle:check required
• [x] Static Analysis: mvn -P lint clean compile pmd:cpd-check spotbugs:check advisory only
• [ ] This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample
• [ ] This sample adds a new Product API, and I updated the Blunderbuss issue/PR auto-assigner with the codeowners for this sample
• [X] Please merge this PR for me once it is approved

[snippet-bot[bot]]

Here is the summary of changes.

You are about to add 2 region tags.

• auth/src/main/java/com/google/cloud/auth/samples/ApiKeyAuthExample.java:19, tag auth_cloud_api_key
• auth/src/main/java/com/google/cloud/auth/samples/ApiKeyAuthExample.java:33, tag auth_cloud_api_key

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