Postgres 18 Beta Dockerfile

Builds the Postgres 18 beta from source so that it can be tested using docker.

To use, clone this repo locally, open a terminal in the repo directory and run docker build -t postgres:18-beta1 .. After the build completes, you can run the image and configure it using the same environment variables used in the standard Postgres image, e.g. docker run --rm -p 5432:5432 -e POSTGRES_USER=postgres -e POSTGRES_PASSWORD=postgre s postgres:18-beta1.

Important! This performs a basic build of Postgres using the default configuration. If want to enabled additional features you can tweak the build by following the Postgres build documentation.