Add ADBC for Python client examples

https://arrow.apache.org/flight-sql-postgresql/current/client.html
We have ADBC (C API) client examples but Python API will be also useful.

Start by reading the linked Flight SQL client documentation and locating the existing ADBC C API examples it references. Add corresponding Python API client examples, with completion shown by the examples appearing alongside the existing documentation.

索引モデルが issue の本文から書いたものです。