chore: update GitHub Actions workflow to trigger on main branch pushes and add concurrency settings

.github/workflows/docker_build.yaml

@@ -1,6 +1,12 @@
 name: Build and Push Docker Images
 
 on:
+  push:
+    branches:
+      - main
+    paths:
+      - 'surfsense_backend/**'
+      - 'surfsense_web/**'
   workflow_dispatch:
     inputs:
       branch:
@@ -8,6 +14,10 @@ on:
         required: false
         default: ''
 
+concurrency:
+  group: docker-build
+  cancel-in-progress: false
+
 permissions:
   contents: write
   packages: write