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/exportarr/Dockerfile

@@ -11,11 +11,8 @@ 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/onedr0p/exportarr/releases/download/v${PACKAGE_VERSION}/exportarr_${PACKAGE_VERSION}_linux_amd64.tar.gz | tar --strip-components=1 -xzf -
-
 # Default command to build RPMs
 CMD /app/resources/build.sh