Add CI integration with drone

.drone.yml

@@ -0,0 +1,39 @@
+kind: pipeline
+name: backend
+
+steps:
+- name: backend
+  image: plugins/docker
+  settings:
+    repo: caminsha/lettergen-backend
+    context: ./backend
+    dockerfile: ./backend/Dockerfile.prod
+    username:
+      from_secret: DOCKER_USERNAME
+    password:
+      from_secret: DOCKER_SECRET
+  when:
+    branch:
+      - main
+    event:
+      - push
+---
+kind: pipeline
+name: frontend
+
+steps:
+- name: frontend
+  image: plugins/docker
+  settings:
+    repo: caminsha/lettergen-frontend
+    context: ./frontend
+    dockerfile: ./frontend/Dockerfile.prod
+    username:
+      from_secret: DOCKER_USERNAME
+    password:
+      from_secret: DOCKER_SECRET
+  when:
+    branch:
+      - main
+    event:
+      - push