Create Materialize quickstart examples

[ianmcook]

Under each postgresql subdirectory, create a materialize subdirectory that contains an example specifically for Materialize.

[ianmcook]

For context: There was previously a problem that prevented the Postgres ADBC driver from working with Materialize. This was fixed in MaterializeInc/materialize#37896 and documented in MaterializeInc/materialize#38535 (albeit using pip to install the driver from PyPI instead of using dbc to install the driver from the registry).

We should mention in the markdown that this requires Materialize v26.40 or later.

[ianmcook]

For the quickstarts, use the Materialize Emulator Docker image as described at https://materialize.com/docs/get-started/install-materialize-emulator/.