databases/postgresql18-*: Update to 18.0

PostgreSQL 18 improves performance for workloads of all sizes through a
new I/O subsystem that has demonstrated up to 3× performance
improvements when reading from storage, and also increases the number of
queries that can use indexes. This release makes major-version upgrades
less disruptive, accelerating upgrade times and reducing the time
required to reach expected performance after an upgrade completes.
Developers also benefit from PostgreSQL 18 features, including virtual
generated columns that compute values at query time, and the
database-friendly uuidv7() function that provides better indexing and
read performance for UUIDs. PostgreSQL 18 makes it easier to integrate
with single-sign on (SSO) systems with support for OAuth 2.0
authentication.

Release notes: https://www.postgresql.org/about/news/postgresql-18-released-3142/