iambic setup does not pre-flight whether there were conflicting IambicSpokeRole during AWS setup

[smoy]

Describe the bug
iambic setup can fail to complete for AWS setup if there are conflicting IambicHubRole or IambicSpokeRole because AWS IAM Role name within an account must be unique.

The conflict typically comes from a previous failed iambic setup. Because there are not iambic uninstall, the operator has to manually clean up any conflicting AWS IAM Role.

To Reproduce

1. Create a AWS IAM Role name IambicSpokeRole or IambicHubRole in the mgmt account.
2. Run iambic setup
3. It will fail to create Stack either on mgmt account or any of the org member account.
4. See error

Expected behavior

1. iambic setup either preflight if there are any conflicting IAM role before attempting to create the stack.
2. iambic cleanup that can remove any conflicting resources for the AWS setup.

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