build: halt build if PG can have a minor upgrade (#187)

When building a system image, we start from a community postgres image.
There is the chance that newer postgres packages are released, and they
could be upgraded when installing the supported extensions. We want to
prevent this scenario, as it could lead to unexpected versions in the
container image.

Closes #186

Signed-off-by: Francesco Canovai <francesco.canovai@enterprisedb.com>

Debian/Dockerfile.template

@@ -31,6 +31,11 @@ COPY requirements.txt /
 # Install additional extensions
 RUN set -xe; \
 	apt-get update; \
+	if apt list --upgradable 2>/dev/null | grep -q '^postgres'; then \
+		echo "ERROR: Upgradable postgres packages found!"; \
+		apt list --upgradable 2>/dev/null | grep '^postgres'; \
+		exit 1; \
+	fi; \
 	apt-get install -y --no-install-recommends \
 		"postgresql-${PG_MAJOR}-pgaudit" \
 		"postgresql-${PG_MAJOR}-pgvector" \