feat: add max-attempts and retry-mode input parameters

[AdunSG]

Summary

• Adds max-attempts and retry-mode as action input parameters to configure AWS SDK retry behavior
• Passes these values to the CloudFormationClient (and S3Client) constructor config
• Allows users to control retry behavior without relying on AWS_MAX_ATTEMPTS and AWS_RETRY_MODE environment variables, which are global and can bleed into other workflow steps

Motivation

There was no way to configure the SDK-level retry behavior from the action inputs. Users had to set environment variables outside the action context, which is not discoverable and affects the entire job.

Changes

• action.yml: Added max-attempts and retry-mode input definitions
• src/utils.ts: Added parseRetryMode() validator (accepts 'standard' or 'adaptive')
• src/validation.ts: Added both fields to the base schema (applies to all modes)
• src/main.ts: Reads inputs and sets maxAttempts/retryMode on the shared client configuration

Test plan

• All existing tests pass (212 tests, 6 suites)
• TypeScript compiles without errors
• dist/index.js rebuilt successfully
• Verify with a workflow using max-attempts: 10 and retry-mode: adaptive

🤖 Generated with Claude Code

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Please notice that although i created this PR using Claude Code i did review the changes myself and the need for this feature is real. Highly parallelized stack deployment can cause issues with Rate Excceeded errors.

[kddejong]

Thanks for the contribution — the feature makes sense and the implementation is clean. A few things needed before we can merge:

Missing tests: parseRetryMode in src/utils.ts needs unit tests covering:

• Valid inputs ('standard', 'adaptive') return the expected value
• Invalid input (e.g. 'exponential') throws with the expected error message
• Empty string / undefined returns undefined

The validation schema changes should also have test coverage confirming max-attempts and retry-mode are parsed correctly through validateAndParseInputs.

[AdunSG]

There was no existing test for validateAndParseInputs() i had to add a new file for that. It now only covers the new retryMode and maxAttempts value validation.
Tests for parseRetryMode() have been added to utils.test.ts