chore(ci): trigger aws builds on push on main

.github/workflows/start_aws_builds.yml

@@ -0,0 +1,38 @@
+# Start all AWS build jobs on Slab CI bot.
+name: Start all AWS builds
+
+on:
+  push:
+    branches:
+      - 'main'
+    tags:
+      - 'v*'
+  workflow_dispatch:
+
+jobs:
+  start-builds:
+    strategy:
+      matrix:
+        command: [cpu-build, gpu-build]
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout Slab repo
+        uses: actions/checkout@v3
+        with:
+          repository: zama-ai/slab
+          path: slab
+          token: ${{ secrets.CONCRETE_ACTIONS_TOKEN }}
+
+      - name: Start AWS job in Slab
+        shell: bash
+        # TODO: step result must be correlated to HTTP return code.
+        run: |
+          echo -n '{"command": "${{ matrix.command }}", "git_ref": "${{ github.ref }}", "sha": "${{ github.sha }}"}' > command.json
+          SIGNATURE="$(slab/scripts/hmac_calculator.sh command.json '${{ secrets.JOB_SECRET }}')"
+          curl -v -k \
+          -H "Content-Type: application/json" \
+          -H "X-Slab-Repository: ${{ github.repository }}" \
+          -H "X-Slab-Command: start_aws" \
+          -H "X-Hub-Signature-256: sha256=${SIGNATURE}" \
+          -d @command.json \
+          ${{ secrets.SLAB_URL }}