fix: catch AuthError to an informative message

[pbrisbin]

Before,

% AWS_PROFILE=x stack exec -- stackctl cat
CredentialChainExhausted

Now,

% AWS_PROFILE=x stack exec -- stackctl cat
2025-10-17 18:31:44 [error    ] No AWS credentials were found in your environment.
                                For details of where stackctl looks for credentials, see:
                                https://hackage.haskell.org/package/amazonka-2.0/docs/Amazonka-Auth.html#v:discover
                                exception=CredentialChainExhausted

[chris-martin]

Beautiful. I wonder if this should be upstreamed to be Amazonka's responsibility, because I want this behavior everywhere.

[pbrisbin]

I wonder if this should be upstreamed

Depends on what you mean by "this". If you just mean improving displayException to include a little more details for this exception, that would make sense to me. We would still be doing things on our end to catch-log-exit, which I think should remain in the realm of library client.

[chris-martin]

Yes, I mean rather than having to link to docs, that description should be embedded in the displayException output for any user of amazonka to be able to print it.