Add sample rails + postgresql application

Signed-off-by: Alex Koch <alex@esparklearning.com>

rails-postgres/app/Dockerfile

@@ -0,0 +1,18 @@
+FROM ruby:3.1
+
+WORKDIR /app
+
+RUN useradd -m app && chown app:app /app
+
+RUN apt-get update -qq && apt-get install -y --no-install-recommends postgresql-client
+
+USER app
+
+COPY --chown=app:app Gemfile* .
+RUN bundle install
+
+COPY --chown=app:app . .
+
+EXPOSE 3000
+
+CMD ["bundle", "exec", "rails", "server", "-b", "0.0.0.0"]