Several Issues on Iceberg about frostdb

[thorfour]

Hey! Glad you're excited to use Iceberg too! This is still my active project so there's still work to be done before I'd recommend it for production use. However as for the issues you've raised.

1. This is supported now with the latest changes I've made in #839

2. Yes! Iceberg maintenance is what I'm currently working on. I have expiry of metadata, and snapshots working. But need to also implement cleaning orphaned files as well as a way to age out data. So this is coming!

[jicanghaixb]

Thank you for your reply and excellent job! now frostdb iceberg support manifest and manifestEntry filter, it would be even better if support for rowgroup filters could be enhanced.
example: consider an unordered column with a high dimension. If filtering is only done through upper and lower bounds, there will still be useless rowgroups that are read too much. frostdb supports column bloom filtering, but the property of column sorting must be set. sorting columns with a high dimension may consume a lot of resources. can we set sorting and bloom to not be strongly bound by schema.

[thorfour]

Block expiry has been implemented with the above PR to add a maintenance ability to the Iceberg storage engine.