refactor(iam): update IAM policy samples to use GAPIC library

[ssvir]

… rewrote using a new library

Description

Fixes

Note: Before submitting a pull request, please open an issue for discussion if you are not associated with Google.

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

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[Sita04]

@ssvir PTAL at the lint errors and sign the CLA here: https://cla.developers.google.com/

[snippet-bot[bot]]

Here is the summary of changes.

You are about to add 4 region tags.

- [iam/api-client/src/main/java/iam/snippets/GetProjectPolicy.java:18](https://github.com/GoogleCloudPlatform/java-docs-samples/blob/26c0d6ff4a338070a6c01d38e6f63930c15630c2/iam/api-client/src/main/java/iam/snippets/GetProjectPolicy.java#L18), tag `iam_get_policy` - [iam/api-client/src/main/java/iam/snippets/GetServiceAccountPolicy.java:18](https://github.com/GoogleCloudPlatform/java-docs-samples/blob/26c0d6ff4a338070a6c01d38e6f63930c15630c2/iam/api-client/src/main/java/iam/snippets/GetServiceAccountPolicy.java#L18), tag `iam_service_account_get_policy` - [iam/api-client/src/main/java/iam/snippets/SetProjectPolicy.java:18](https://github.com/GoogleCloudPlatform/java-docs-samples/blob/26c0d6ff4a338070a6c01d38e6f63930c15630c2/iam/api-client/src/main/java/iam/snippets/SetProjectPolicy.java#L18), tag `iam_set_policy` - [iam/api-client/src/main/java/iam/snippets/SetServiceAccountPolicy.java:18](https://github.com/GoogleCloudPlatform/java-docs-samples/blob/26c0d6ff4a338070a6c01d38e6f63930c15630c2/iam/api-client/src/main/java/iam/snippets/SetServiceAccountPolicy.java#L18), tag `iam_service_account_set_policy`

You are about to delete 2 region tags.

- [iam/api-client/src/main/java/iam/snippets/GetPolicy.java:18](https://github.com/GoogleCloudPlatform/java-docs-samples/blob/a3202ac8b0a4a1ab3e11c447bb6eea687111aa76/iam/api-client/src/main/java/iam/snippets/GetPolicy.java#L18), tag `iam_get_policy` - [iam/api-client/src/main/java/iam/snippets/SetPolicy.java:18](https://github.com/GoogleCloudPlatform/java-docs-samples/blob/a3202ac8b0a4a1ab3e11c447bb6eea687111aa76/iam/api-client/src/main/java/iam/snippets/SetPolicy.java#L18), tag `iam_set_policy`

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