refactor: move download logic from Dockerfiles to build.sh scripts

Move complex download commands from Dockerfiles to build.sh scripts for consistency:
- pgbouncer_exporter, bind_exporter, exportarr, node_exporter, postgres_exporter: GitHub downloads
- vmagent, vmalert: VictoriaMetrics vmutils downloads
- vminsert, vmselect, vmstorage: VictoriaMetrics cluster downloads

All Dockerfiles now follow the simple template pattern with download logic properly contained in build scripts.

rpms/postgres_exporter/Dockerfile

@@ -11,11 +11,9 @@ ENV PACKAGE_RELEASE=${PACKAGE_RELEASE}
 ARG PACKAGE_VERSION
 ENV PACKAGE_VERSION=${PACKAGE_VERSION}
 
-# Copy nfpm.yaml from the context into the container
+# Copy resources from the context into the container
 COPY resources /app/resources
 
-# Download the required files
-RUN 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 -
 
 # Default command to build RPMs
 CMD /app/resources/build.sh

rpms/postgres_exporter/resources/build.sh

@@ -1,2 +1,6 @@
 #!/usr/bin/bash
+
+# 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