update building with individual number

.drone.jsonnet

@@ -8,7 +8,7 @@
         name: 'builder',
         image: 'plugins/docker',
         settings: {
-          tags: ['builder'],
+          tags: ['builder-${DRONE_BUILD_NUMBER}'],
           dockerfile: 'Dockerfile.builder',
           registry: 'gitea.pb42.de',
           repo: 'gitea.pb42.de/matthias/reflex-ipad',
@@ -19,12 +19,25 @@
       },
       {
         name: 'frontend-builder',
-        image: 'gitea.pb42.de/matthias/reflex-ipad:builder',
+        image: 'gitea.pb42.de/matthias/reflex-ipad:builder-${DRONE_BUILD_NUMBER}',
         pull: 'always',
         commands: [
           'cd /app',
           'reflex export --frontend-only --no-zip',
           'mv .web/_static /drone/src/web',
+          'mv .web/_static /drone/src/web',
+        ],
+        depends_on: [
+          'builder',
+        ],
+      },
+      {
+        name: 'dockerfile-builder',
+        image: 'alpine',
+        pull: 'always',
+        commands: [
+          'apk add --update sed',
+          'sed -i Dockerfile.backend -e "s/#BUILDNR#/${DRONE_BUILD_NUMBER}/"',
         ],
         depends_on: [
           'builder',
@@ -37,6 +50,7 @@
           tags: ['backend-latest'],
           dockerfile: 'Dockerfile.backend',
           registry: 'gitea.pb42.de',
+          cache_from: 'gitea.pb42.de/matthias/reflex-ipad:backend-latest',
           repo: 'gitea.pb42.de/matthias/reflex-ipad',
           config: { from_secret: 'dockerconfigjson' },
           build_args: ['API_URL=https://ipad.pb42.de'],
@@ -44,6 +58,7 @@
         },
         depends_on: [
           'builder',
+          'dockerfile-builder',
         ],
       },
       {