actions: Use Ubicloud instead of self-hosted

Makes use of managed Ubicloud runners for multi-platform builds rather than relying on self-hosted actions runners
x86 and arm builds are built concurrently on sepatate runners and marged at the end.

https://www.ubicloud.com/docs/github-actions-integration/quickstart

.github/workflows/docker.yml

@@ -0,0 +1,117 @@
+name: Build
+
+on:
+  workflow_dispatch:
+  push:
+    branches:
+      - '*'
+
+env:
+  IMAGE_NAME: ghcr.io/yuuki-discord/yuuki-bot
+jobs:
+  docker:
+    name: Docker ${{ matrix.platform }}
+    runs-on: ${{ matrix.runner }}
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - runner: ubicloud-standard-2
+            platform: linux/amd64
+          - runner: ubicloud-standard-2-arm
+            platform: linux/arm64,linux/arm/v6,linux/arm/v7
+
+    steps:
+      - name: Check out code
+        uses: actions/checkout@v4
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - 
+        name: Login to GitHub Registry
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.repository_owner }}
+          password: ${{ secrets.PAT }}
+
+      - name: Extract metadata for Docker
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ${{ env.IMAGE_NAME }}
+          tags: |
+            type=sha,prefix=
+            type=ref,event=branch
+            type=raw,value=latest,enable={{is_default_branch}}
+            type=semver,pattern={{version}}
+            type=semver,pattern={{major}}.{{minor}}
+
+      - name: Build and push by digest
+        id: build
+        uses: docker/build-push-action@v5
+        if: github.ref == 'refs/heads/master'
+        with:
+          context: .
+          platforms: ${{ matrix.platform }}
+          labels: ${{ steps.meta.outputs.labels }}
+          cache-from: type=gha,scope=ubicloud-${{ matrix.runner }}
+          cache-to: type=gha,mode=max,scope=ubicloud-${{ matrix.runner }}
+          outputs: type=image,name=${{ env.IMAGE_NAME }},push-by-digest={{is_default_branch}},name-canonical={{is_default_branch}},push={{is_default_branch}}
+          provenance: false
+
+      - name: Export digest
+        if: github.ref == 'refs/heads/master'
+        run: |
+          mkdir -p /tmp/digests
+          digest="${{ steps.build.outputs.digest }}"
+          touch "/tmp/digests/${digest#sha256:}"
+
+      - name: Upload digest
+        if: github.ref == 'refs/heads/master'
+        uses: actions/upload-artifact@v4
+        with:
+          name: digests-${{ matrix.runner }}
+          path: /tmp/digests/*
+          if-no-files-found: error
+          retention-days: 1
+
+  merge:
+    if: github.ref == 'refs/heads/master'
+    runs-on: ubicloud
+    needs:
+      - docker
+    steps:
+      - name: Download digests
+        uses: actions/download-artifact@v4
+        with:
+          pattern: digests-*
+          merge-multiple: true
+          path: /tmp/digests
+      - 
+        name: Login to GitHub Registry
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.repository_owner }}
+          password: ${{ secrets.PAT }}
+      - name: Docker meta
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ${{ env.IMAGE_NAME }}
+          tags: |
+            type=sha,prefix=
+            type=ref,event=branch
+            type=raw,value=latest,enable={{is_default_branch}}
+            type=semver,pattern={{version}}
+            type=semver,pattern={{major}}.{{minor}}
+      - name: Create manifest list and push
+        working-directory: /tmp/digests
+        run: |
+          docker buildx imagetools create $(jq -cr '.tags | map("-t " + .) | join(" ")' <<< "$DOCKER_METADATA_OUTPUT_JSON") \
+            $(printf '${{ env.IMAGE_NAME }}@sha256:%s ' *)
+      - name: Inspect image
+        run: |
+          docker buildx imagetools inspect ${{ env.IMAGE_NAME }}:${{ steps.meta.outputs.version }}