Two medium-priority issues gemini flagged on the read-only IAM API:
1. The static-config bootstrap was setting CreatedAt = time.Now() on
every server start, so the IAM GetOpenIDConnectProvider response's
CreateDate shifted on each restart even when backed by a persistent
store. Look up the existing record via GetProviderByARN first and
preserve its CreatedAt; only the UpdatedAt advances.
2. FilerOIDCProviderStore.ListProviders had a hardcoded Limit: 1000
that silently truncated above that. Stream-paginate via
StartFromFileName, returning io.EOF naturally and surfacing all
other errors instead of swallowing them.
Addresses two gemini medium reviews on PR #9319.
ef1acaa98c