DOCS: Clearly document unsupported Iceberg Features

[sungwy]

Feature Request / Improvement

Some features that users expect from an Iceberg Client (like https://github.com/apache/iceberg-python/issues/1084) are not yet implemented in PyIceberg, leading to much wasted time from our users.

It will be helpful to clearly document what features are not yet supported on Iceberg to minimize frustration and wasted effort from our community.

[Gowthami03B]

Since this list is always going to be extensive and bound to changes, we can add a section in the docs that points to a say unsupported-features.md in the github repo ?

[github-actions[bot]]

This issue has been automatically marked as stale because it has been open for 180 days with no activity. It will be closed in next 14 days if no further activity occurs. To permanently prevent this issue from being considered stale, add the label 'not-stale', but commenting on the issue is preferred when possible.

[kevinjqliu]

This is partial done by https://iceberg.apache.org/status/ which we should update after 0.9.0 is officially released