gha: retrieve secret from aws secrets manager

[andrewhsu]

jira: DEVPROD-3955

Retrieve secret from AWS secrets manager instead of github repo secret.

[CLAassistant]

All committers have signed the CLA.

[andrewhsu]

error message is by design of the anthropics/claude-code-action@v1 action:

Error: Action failed with error: Workflow validation failed. The workflow file must exist and have identical content to the version on the repository's default branch. If you're seeing this on a PR when you first add a code review workflow file to your repository, this is normal and you should ignore this error.

can ignore this message because after merge the workflow will run if subsequent PRs don't also modify the workflow file.