CLI: Setup AWS missing parameters during setup/export

[MonkeyCanCode]

Added the two missing fields (endpoint_internal and sts_endpoint) that got loss during setup apply/export. As we are using an valid S3 endpoint value ("https://s3.us-west-2.amazonaws.com") in site/content/guides/assets/polaris/reference-setup-config.yaml, I am setting endpoint_internal to "https://bucket.vpce-1a2b3c4d-5e6f.s3.us-west-2.vpce.amazonaws.com" (sample value obtained from https://docs.aws.amazon.com/AmazonS3/latest/userguide/privatelink-interface-endpoints.html but with region change from us-east-1 to us-west-2 for consistency).

Also, I added a test in test_catalogs_command.py to cover S3/STS endpoints are optional and they are are getting process correctly. The fall-back logic for sts_endpoint is not covered here as those are covered on the server side (but I added a comment in site/content/guides/assets/polaris/reference-setup-config.yaml to mention how the fall-back works).

Checklist

• 🛡️ Don't disclose security issues! (contact security@apache.org)
• 🔗 Clearly explained why the changes are needed, or linked related issues: Fixes #
• 🧪 Added/updated tests with good coverage, or manually tested (and explained how)
• 💡 Added comments for complex logic
• 🧾 Updated CHANGELOG.md (if needed)
• 📚 Updated documentation in site/content/in-dev/unreleased (if needed)

[flyrain]

Thanks @MonkeyCanCode !