MotherDuck support

[JelteF]

• Single PG role connected to a single MD user (user may have multiple concurrent PG connections)

• Table support: user’s MD catalog is synchronized with PG (every x second)

  • MD tables created in MD should be reflected in PG (using CREATE TABLE or CREATE TABLE … AS)
  • MD tables created in PG should be reflected in MD
  • MD tables modified in MD should be reflected in PG
  • Support multiple MD databases by encoding db+schema inside the schemaname ddb$db$schema pattern

• Users need to choose a designated PG Database for MD synchronization

• DDL fails in MD/DuckDB, then it should be rolled back in PG

[JelteF]

Fixed by #267