fix: create config file before fpm RPM packaging (#5924)

The RPM build step fails because fpm's --config-files flag requires
/etc/default/rustfs to exist in the staging area, but unlike the DEB
build (which creates it in its package directory structure), the fpm
command has no prior step creating this file.

Create the config file in a temporary directory and pass it to fpm
via a source=dest mapping, matching the DEB build's behavior.

.github/workflows/package.yml

@@ -322,6 +322,17 @@ jobs:
           sudo apt-get update && sudo apt-get install -y ruby ruby-dev build-essential
           sudo gem install fpm
 
+          # Create config file for fpm (DEB build creates it in its package dir structure,
+          # but fpm needs the file to exist before packaging)
+          mkdir -p ./tmp-pkg/etc/default
+          cat > ./tmp-pkg/etc/default/rustfs << 'ENVEOF'
+          # RustFS Environment Configuration
+          # See https://rustfs.com/docs/ for more information
+          # RUSTFS_VOLUMES=""
+          # RUSTFS_ROOT_USER=""
+          # RUSTFS_ROOT_PASSWORD=""
+          ENVEOF
+
           fpm -s dir -t rpm \
             --name rustfs \
             --version "$VERSION" \
@@ -362,6 +373,7 @@ jobs:
             ) \
             --config-files /etc/default/rustfs \
             ./bin/rustfs=/usr/bin/rustfs \
+            ./tmp-pkg/etc/default/rustfs=/etc/default/rustfs \
             deploy/build/rustfs.service=/lib/systemd/system/rustfs.service \
             LICENSE=/usr/share/doc/rustfs/LICENSE \
             README.md=/usr/share/doc/rustfs/README.md