Add configuration for upload purging

Signed-off-by: Richard Scothern <richard.scothern@gmail.com>

cmd/registry/config.yml

@@ -9,6 +9,9 @@ storage:
         layerinfo: inmemory
     filesystem:
         rootdirectory: /tmp/registry-dev
+    maintenance:
+        uploadpurging:
+            enabled: false
 http:
     addr: :5000
     secret: asecretforlocaldevelopment
@@ -39,3 +42,4 @@ notifications:
           threshold: 10
           backoff: 1s
           disabled: true
+