Support static stability for credentials

[richardwang1124]

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1. To make sure we include your contribution in the release notes, please make sure to add description entry for your changes in the "unreleased changes" section of the CHANGELOG.md file (at corresponding gem). For the description entry, please make sure it lives in one line and starts with Feature or Issue in the correct format.

2. For generated code changes, please checkout below instructions first:
   https://github.com/aws/aws-sdk-ruby/blob/version-3/CONTRIBUTING.md

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[github-actions]

Detected 15 possible performance regressions:

• aws-sdk-cloudwatchlogs.put_log_events_small_allocated_kb - z-score regression: 56.66 -> 57.06. Z-score: Infinity
• aws-sdk-cloudwatchlogs.put_log_events_large_allocated_kb - z-score regression: 5990.62 -> 5991.01. Z-score: Infinity
• aws-sdk-cloudwatchlogs.get_log_events_small_allocated_kb - z-score regression: 52.17 -> 52.57. Z-score: Infinity
• aws-sdk-cloudwatchlogs.get_log_events_large_allocated_kb - z-score regression: 7607.98 -> 7608.38. Z-score: Infinity
• aws-sdk-cloudwatchlogs.filter_log_events_large_allocated_kb - z-score regression: 7804.05 -> 7804.45. Z-score: Infinity
• aws-sdk-cloudwatch.put_metric_data_small_allocated_kb - z-score regression: 47.99 -> 48.41. Z-score: 19.31
• aws-sdk-dynamodb.get_item_small_allocated_kb - z-score regression: 72.34 -> 72.74. Z-score: Infinity
• aws-sdk-dynamodb.get_item_large_allocated_kb - z-score regression: 19164.15 -> 19164.54. Z-score: Infinity
• aws-sdk-dynamodb.put_item_small_allocated_kb - z-score regression: 79.71 -> 80.11. Z-score: Infinity
• aws-sdk-dynamodb.put_item_large_allocated_kb - z-score regression: 11937.5 -> 11937.9. Z-score: Infinity
• aws-sdk-dynamodb.batch_get_item_large_allocated_kb - z-score regression: 17569.28 -> 17569.68. Z-score: Infinity
• aws-sdk-kinesis.put_record_small_allocated_kb - z-score regression: 47.95 -> 48.35. Z-score: 143.52
• aws-sdk-kinesis.put_record_large_allocated_kb - z-score regression: 163.96 -> 164.36. Z-score: 143.52
• aws-sdk-sns.publish_small_allocated_kb - z-score regression: 57.75 -> 58.15. Z-score: Infinity
• aws-sdk-sns.publish_large_allocated_kb - z-score regression: 457.95 -> 458.35. Z-score: Infinity