[cchu-ld]

Requirements

• I have added test coverage for new or changed functionality
• I have followed the repository's pull request submission guidelines
• I have validated my changes against all supported platform versions

Related issues

This PR is part 2 of a stack of 7 PRs for ldcli aws-devops-agent. It goes on PR 1 of the stack. Review and merge the PRs in order.

1. feat: ask which existing agent space to connect LaunchDarkly to #903 Agent space choice
2. feat: add AWS regions, send the API version, and shorten credential errors #904 Regions, API version, credential error (this PR)
3. feat: offer to run aws sso login when SSO credentials expire #905 aws sso login offer
4. feat: show names and states in the plaintext status output #906 Readable status output
5. feat: show the setup plan and ask before setup changes AWS #907 Setup plan and confirmation
6. feat: run the setup plan that setup showed #908 Run the shown plan
7. feat: choose the setup steps by who made the agent space #909 Ownership rule and existing spaces

Describe the solution you've provided

• setup accepts 15 regions, up from 11. The new regions are us-east-2, ap-northeast-2, eu-west-3, and eu-north-1.
• The token check sends LD-API-Version: 20240415.
• The credential error does not show the AWS SDK cause. It lists at most 5 profile names and points to aws configure list-profiles. errors.Unwrap still returns the cause.

Describe alternatives you've considered

None.

Additional context

Testing: go test ./... and golangci-lint pass on this branch.

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