Add built-in databaseRename option for snapshot jobs

Goal

Allow users to rename databases during snapshot creation without writing custom preprocessing scripts. This is a common need when the source database name differs from what's expected in dev/test
environments.

TODO / How to implement

• Add a databaseRename option to physicalSnapshot and logicalSnapshot job configs (map of oldName: newName)
• During snapshot, spin up a temporary Postgres container and execute ALTER DATABASE ... RENAME TO ... for each mapping
• Best-effort Postgres shutdown on teardown to keep snapshot jobs robust
• Update example configs to document the new option

Acceptance criteria

• databaseRename config is accepted in both physical and logical snapshot jobs
• Databases are renamed before the snapshot is finalized
• Unit and integration tests pass
• Existing snapshots without databaseRename are unaffected