puppet: Factor out $::architecture case statement for golang.

(cherry picked from commit 788daa953b)

puppet/zulip/manifests/common.pp

@@ -33,6 +33,11 @@ class zulip::common {
 
   $total_memory_mb = Integer($::memorysize_mb)
 
+  $goarch = $::architecture ? {
+    'amd64'   => 'amd64',
+    'aarch64' => 'arm64',
+  }
+
   $versions = {
     # https://github.com/cactus/go-camo/releases
     'go-camo' => {