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/node_exporter/resources/build.sh

@@ -1,6 +1,11 @@
 #!/usr/bin/bash
 
+set -e
+
 # Download the required files
 curl --output - -L https://github.com/prometheus/node_exporter/releases/download/v${PACKAGE_VERSION}/node_exporter-${PACKAGE_VERSION}.linux-amd64.tar.gz | tar --strip-components=1 -xzf -
 
-nfpm pkg --config /app/resources/nfpm.yaml --target /app/dist --packager rpm
+# Process the nfpm.yaml template with environment variables
+envsubst < /app/resources/nfpm.yaml > /app/nfpm.yaml
+
+nfpm pkg --config /app/nfpm.yaml --target /app/dist --packager rpm