More proper Sesame integration

[KinanBab]

Policy language

• [ ] Handle custom Rust policies from Sesame
• [ ] Check policy and annotation consistency more generically
• [ ] Better protocol for sending back policy metadata to Sesame; consider an added ResultSet

Policy construction

• [ ] Probably better to do construction at lower-level (e.g. in k9db::sql::rocksdb) instead of in k9db::shards
• [ ] Fix known bug with policy construction with non-view and non-direct projections

Policy + Dataflow

• [ ] Aggregate operator does not combine or preserve policies for keys, only for aggregates
• [ ] Consider adjustable style for whether policy failures are early detected, and whether they are reported as errors or hidden from returned set

Merges:

• [ ] Cherry pick support for COUNT DISTINCT to main (HIGH PRIORITY)