Add builder workflow

Signed-off-by: Nikolaos Karaolidis <nick@karaolidis.com>

builder.yaml

@@ -0,0 +1,39 @@
+name: Build Builder Image
+
+on:
+  workflow_call:
+    inputs:
+      image:
+        description: "Full image name to build and push"
+        required: true
+        type: string
+
+    secrets:
+      registry_user:
+        required: true
+
+      registry_password:
+        required: true
+
+jobs:
+  builder:
+    runs-on: nix
+    steps:
+      - name: Checkout Repository
+        uses: actions/checkout@v3
+
+      - name: Log In to Registry
+        run: |
+          buildah login -u "${{ secrets.registry_user }}" --password "${{ secrets.registry_password }}" "$(echo "${{ inputs.image }}" | cut -d/ -f1)"
+
+      - name: Pull Builder Cache
+        run: |
+          buildah pull ${{ inputs.image }} || true
+
+      - name: Build Builder Image
+        run: |
+          buildah build --layers -f .gitea/Containerfile -t ${{ inputs.image }} .
+
+      - name: Push Builder Image
+        run: |
+          skopeo copy containers-storage:${{ inputs.image }} docker://${{ inputs.image }}