chore: remove docker build & push on PRs (#7805)

We did this to validate that yarn 4 works and that has now been used for
a while. Lets stop pushing all PRs now

.github/workflows/build_docker_prs.yaml

@@ -1,47 +0,0 @@
-name: PR -> Docker build
-
-on:
-  pull_request:
-
-jobs:
-  build:
-    runs-on: ubuntu-latest
-    strategy:
-      matrix:
-        version: [ 20.14.0-alpine ]
-    steps:
-      - name: Checkout
-        uses: actions/checkout@v4
-      - name: Setup QEmu
-        uses: docker/setup-qemu-action@v3
-      - name: Setup Docker buildx
-        uses: docker/setup-buildx-action@v3
-      - name: Docker meta configuration
-        uses: docker/metadata-action@v5
-        id: meta
-        with:
-          images: |
-            unleashorg/unleash-server
-          tags: |
-            # only enabled for workflow dispatch except main (assume its a release):
-            type=semver,pattern={{ version }},enable=${{ github.event_name == 'workflow_dispatch' && github.ref != 'refs/heads/main' }},value=${{ inputs.version }}
-            type=semver,pattern={{ major }}.{{ minor }},enable=${{ github.event_name == 'workflow_dispatch' && github.ref != 'refs/heads/main' }},value=${{ inputs.version }}
-            type=semver,pattern={{ major }},enable=${{ github.event_name == 'workflow_dispatch' && github.ref != 'refs/heads/main' }},value=${{ inputs.version }}
-            # only enabled in main:
-            type=edge,prefix=main-,suffix=-${{ matrix.version }},enable=${{ github.ref == 'refs/heads/main' }}
-            # only enabled on workflow_dispatch:
-            type=sha,suffix=-${{ matrix.version }},enable=${{ github.event_name == 'workflow_dispatch' }}
-      - name: Login to docker hub
-        uses: docker/login-action@v3
-        with:
-          username: ${{ secrets.DOCKERHUB_USERNAME }}
-          password: ${{ secrets.DOCKERHUB_TOKEN }}
-      - name: Build tag and push image to Docker hub
-        uses: docker/build-push-action@v6
-        with:
-          context: .
-          platforms: linux/amd64,linux/arm64
-          push: false
-          tags: ${{ steps.meta.outputs.tags }}
-          labels: ${{ steps.meta.outputs.labels }}
-          build-args: NODE_VERSION=${{ matrix.version }}