cull image steps from pr

.drone.yml

@@ -45,6 +45,12 @@ steps:
       context: .
     depends_on:
       - build-backend
+    when:
+      branch:
+        - master
+        - staging
+      event:
+        - push
 
   - name: image-frontend
     image: plugins/docker
@@ -62,6 +68,12 @@ steps:
       context: web
     depends_on:
       - build-frontend
+    when:
+      branch:
+        - master
+        - staging
+      event:
+        - push
 
   - name: image-validator
     image: plugins/docker
@@ -79,6 +91,12 @@ steps:
       context: validation
     depends_on:
       - build-validator
+    when:
+      branch:
+        - master
+        - staging
+      event:
+        - push
 
   - name: deploy
     image: argoproj/argocd:latest
@@ -117,6 +135,6 @@ steps:
         - pull_request
 ---
 kind: signature
-hmac: 7e99b0b7f6826cff9c6b981231fce6c653bb5c12792d8a83d3fea2447be58b3c
+hmac: 81d9b9c8780aaba7712d48363d5162906b88aa45297b4486be8cee06484da474
 
 ...