allow manual releases of v21

Author: sigpwned

.github/workflows/deliver21.yml

@@ -1,6 +1,7 @@
 name: deliver21
 
 on:
+  workflow_dispatch:
   push:
     branches:
       - release/21
@@ -37,4 +38,4 @@ jobs:
         with:
           registry-type: "public"
       - name: Deploy artifacts
-        run: mvn -B clean dependency:copy-dependencies docker:build docker:tag docker:push
+        run: mvn -B clean dependency:copy-dependencies docker:build docker:tag docker:push