feat: add v2 client

[meltsufin]

The commit are broken down to make it clear which parts are autogenerated and which parts had to be manually edited.

[generated-files-bot]

Warning: This pull request is touching the following templated files:

• .github/CODEOWNERS

[suztomo]

CLIRR is failing with removed classes. "beta" marked version is ok to have breaking changes. Would you confirm this intentional? (The CL messages would reveal that)

[INFO] --- clirr-maven-plugin:2.8:check (default-cli) @ proto-google-iam-v2beta ---
[INFO] artifact com.google.api.grpc:proto-google-iam-v2beta: checking for updates from central
[INFO] Comparing to version: 1.5.2
Error:  8001: com.google.iam.v2beta.PolicyName: Class com.google.iam.v2beta.PolicyName removed
Error:  8001: com.google.iam.v2beta.PolicyName$Builder: Class com.google.iam.v2beta.PolicyName$Builder removed

[meltsufin]

CLIRR is failing with removed classes. "beta" marked version is ok to have breaking changes. Would you confirm this intentional? (The CL messages would reveal that)

[INFO] --- clirr-maven-plugin:2.8:check (default-cli) @ proto-google-iam-v2beta ---
[INFO] artifact com.google.api.grpc:proto-google-iam-v2beta: checking for updates from central
[INFO] Comparing to version: 1.5.2
Error:  8001: com.google.iam.v2beta.PolicyName: Class com.google.iam.v2beta.PolicyName removed
Error:  8001: com.google.iam.v2beta.PolicyName$Builder: Class com.google.iam.v2beta.PolicyName$Builder removed

It's not a new failure. You can see the same in main branch: https://github.com/googleapis/java-iam/actions/runs/3026401708/jobs/4869759373.

[suztomo]

Thank you for checking. ci / dependencies (8) failed.

[INFO] --- maven-dependency-plugin:3.3.0:analyze (default-cli) @ proto-google-iam-v2beta ---
Warning:  Unused declared dependencies found:
Warning:     com.google.api.grpc:proto-google-iam-v1:jar:1.5.3-SNAPSHOT:compile
Warning:     com.google.api:api-common:jar:2.2.1:compile
Warning:     com.google.guava:guava:jar:31.1-jre:compile

[suztomo]

Looks good to me. Let's get the checks green.

[suztomo]

Wrong module?

[INFO] --- maven-dependency-plugin:3.3.0:analyze (default-cli) @ proto-google-iam-v2beta ---
Warning:  Unused declared dependencies found:
Warning:     com.google.api.grpc:proto-google-iam-v1:jar:1.5.3-SNAPSHOT:compile
Warning:     com.google.api:api-common:jar:2.2.1:compile
Warning:     com.google.guava:guava:jar:31.1-jre:compile

[meltsufin]

Ah didn't notice that! Thanks!

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