fix(frontend): adjust workflows

Signed-off-by: Tilman Vatteroth <git@tilmanvatteroth.de>

.github/workflows/frontend-docker.yml

@@ -2,17 +2,45 @@
 #
 # SPDX-License-Identifier: AGPL-3.0-only
 
-name: Build Docker Image
+name: Frontend / build docker image
 
 on:
   push:
-    branches: [ main ]
+    branches: [ develop ]
+
+defaults:
+  run:
+    working-directory: frontend
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
 
 jobs:
+  changes:
+    name: Check for frontend changes
+    runs-on: ubuntu-latest
+    permissions:
+      pull-requests: read
+    outputs:
+      changed: ${{ steps.changed.outputs.files }}
+    steps:
+      - name: Check for frontend file changes
+        uses: dorny/paths-filter@v2
+        id: changed
+        with:
+          filters: |
+            files:
+              - 'frontend/**'
+              - '.github/**'
+              - '.yarn/**'
+
   build:
+    needs: changes
     runs-on: ubuntu-latest
     steps:
       - name: Generate Docker metadata
+        if: needs.changes.outputs.changed == 'true'
         id: meta
         uses: docker/metadata-action@v4
         with:
@@ -24,13 +52,15 @@ jobs:
             type=semver,pattern={{major}}
 
       - name: Set up QEMU
+        if: needs.changes.outputs.changed == 'true'
         uses: docker/setup-qemu-action@v2
 
       - name: Set up Docker Buildx
+        if: needs.changes.outputs.changed == 'true'
         uses: docker/setup-buildx-action@v2
 
       - name: Login to GHCR
-        if: github.event_name != 'pull_request'
+        if: github.event_name != 'pull_request' && needs.changes.outputs.changed == 'true'
         uses: docker/login-action@v2
         with:
           registry: ghcr.io
@@ -38,13 +68,15 @@ jobs:
           password: ${{ secrets.GITHUB_TOKEN }}
 
       - name: Build and push
+        if: needs.changes.outputs.changed == 'true'
         uses: docker/build-push-action@v3
         with:
           push: true
-          file: Dockerfile
+          file: frontend/Dockerfile
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}
           cache-from: type=gha
           cache-to: type=gha,mode=max
+          context: .
           build-args: |
             BUILD_VERSION=${{ github.event.head_commit.id }}