refactor: modernise RPM builder with Python tooling v2

- Migrate from legacy shell-based build system to modern Python tooling
- Update all metadata.yaml files to new schema with per-distro builds
- Standardise build scripts with curl -L, envsubst, and error handling
- Convert nfpm.yaml templates to use environment variable substitution
- Update Dockerfile to accept all package metadata as build arguments
- Modernise Makefile to use new Python build tool commands
- Update CI workflow to use tools/build instead of make

rpms/postgres_exporter/resources/build.sh

@@ -1,6 +1,10 @@
 #!/usr/bin/bash
+set -e
 
 # Download the required files
 curl --output - -L https://github.com/prometheus-community/postgres_exporter/releases/download/v${PACKAGE_VERSION}/postgres_exporter-${PACKAGE_VERSION}.linux-amd64.tar.gz | tar --strip-components=1 -xzf -
 
-nfpm pkg --config /app/resources/nfpm.yaml --target /app/dist --packager rpm
+# Process nfpm.yaml with envsubst
+envsubst < /app/resources/nfpm.yaml > /app/nfpm.yaml
+
+nfpm pkg --config /app/nfpm.yaml --target /app/dist --packager rpm

rpms/postgres_exporter/resources/nfpm.yaml

@@ -1,16 +1,16 @@
 # nfpm.yaml
 
-name: postgres_exporter
+name: ${PACKAGE_NAME}
 version: ${PACKAGE_VERSION}
 release: ${PACKAGE_RELEASE}
-arch: amd64
-platform: linux
+arch: ${PACKAGE_ARCH}
+platform: ${PACKAGE_PLATFORM}
 section: default
 priority: extra
-description: "A PostgreSQL metric exporter for Prometheus"
-maintainer: Prometheus
-homepage: https://github.com/prometheus-community/postgres_exporter
-license: Apache-2.0 license
+description: "${PACKAGE_DESCRIPTION}"
+maintainer: ${PACKAGE_MAINTAINER}
+homepage: ${PACKAGE_HOMEPAGE}
+license: ${PACKAGE_LICENSE}
 
 disable_globbing: false