Implement `maxAttempts` inside the RetrySettings for GAPICs

[lqiu96]

RetrySettingsComposer doesn't have logic to create set the maxAttempts value: https://github.com/googleapis/sdk-platform-java/blob/087253a41e8c1e1328710c19505e1198fc755003/gapic-generator-java/src/main/java/com/google/api/generator/gapic/composer/common/RetrySettingsComposer.java#L495-L588 even if it's set in the grpc_service.json file.

Searching through google-cloud-java shows that there aren't any occurrences of setMaxAttempts being generated in the StubSettings: https://github.com/search?q=repo%3Agoogleapis%2Fgoogle-cloud-java%20setMaxAttempts&type=code