Update CI workflow: add support for multiple platforms in Docker build

Author: L4B0MB4

.github/workflows/ui.yml

@@ -55,6 +55,7 @@ jobs:
         with:
           context: .
           file: "./Dockerfile"
+          platforms: linux/amd64,linux/arm64
           push: true
           tags: ${{ vars.DOCKERHUB_USERNAME }}/pryvt_ui:${{ github.ref == 'refs/heads/master' && 'latest' || github.ref_name }}
       - name: Build without push