refactor(compute): create Certificate samples

[ssvir]

implemented : compute_certificate_create, compute_certificate_create_regional

Description

Fixes #

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Checklist

• [ ] I have followed Sample Format Guide
• [ ] pom.xml parent set to latest shared-configuration
• [ ] 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)
• [ ] Tests pass: mvn clean verify required
• [ ] Lint passes: mvn -P lint checkstyle:check required
• [ ] 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
• [ ] 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.

- [compute/load-balancing/src/main/java/compute/CreateCertificate.java:19](https://github.com/GoogleCloudPlatform/java-docs-samples/blob/394ac837ed6b8d56df249541bd5bfec1358c4ae5/compute/load-balancing/src/main/java/compute/CreateCertificate.java#L19), tag `compute_certificate_create` - [compute/load-balancing/src/main/java/compute/CreateRegionalCertificate.java:19](https://github.com/GoogleCloudPlatform/java-docs-samples/blob/394ac837ed6b8d56df249541bd5bfec1358c4ae5/compute/load-balancing/src/main/java/compute/CreateRegionalCertificate.java#L19), tag `compute_certificate_create_regional`

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