chore: nightly serverless-init builds (#1135)

## Overview
We'll be using this to check serverless-init against the latest main
datadog agent nightly.

Author: apiarian-datadog

.github/workflows/nightly-serverless-init.yml

@@ -0,0 +1,117 @@
+name: Nightly serverless-init build
+
+on:
+  schedule:
+    # 2 AM UTC (~9-10 PM ET), daily
+    - cron: "0 2 * * *"
+  workflow_dispatch:
+
+env:
+  IMAGE_NAME: datadog/datadog-lambda-extension/serverless-init
+  REGISTRY: ghcr.io
+
+jobs:
+  build-nightly:
+    runs-on: ubuntu-22.04
+    permissions:
+      contents: read
+      packages: write
+    strategy:
+      matrix:
+        arrays:
+          - { dockerFile: "Dockerfile.serverless-init.build", isAlpine: "false", tagSuffix: "" }
+          - { dockerFile: "Dockerfile.serverless-init.alpine.build", isAlpine: "true", tagSuffix: "-alpine" }
+    name: "Nightly Build (isAlpine: ${{ matrix.arrays.isAlpine }})"
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          repository: DataDog/datadog-agent
+          ref: main
+          path: datadog-agent
+
+      - name: Compute version tags
+        id: meta
+        run: |
+          STAMP=$(date -u +%Y%m%d)
+          SHORT_SHA=$(git -C datadog-agent rev-parse --short=8 HEAD)
+          echo "stamp=${STAMP}" >> "$GITHUB_OUTPUT"
+          echo "short_sha=${SHORT_SHA}" >> "$GITHUB_OUTPUT"
+          echo "version=nightly-${STAMP}-${SHORT_SHA}" >> "$GITHUB_OUTPUT"
+
+      # Pin QEMU to a known-good version. See release-serverless-init.yml
+      # and test-qemu-versions.yml for context on QEMU breakage history.
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@ce360397dd3f832beb865e1373c09c0e9f86d70a # v4.0.0
+        with:
+          image: tonistiigi/binfmt:qemu-v10.1.3
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@4d04d5d9486b7bd6fa91e7baf45bbb4f8b9deedd # v4.0.0
+
+      - name: Build binaries
+        working-directory: ./scripts
+        run: ./build_serverless_init.sh
+        env:
+          AGENT_PATH: datadog-agent
+          VERSION: ${{ steps.meta.outputs.version }}
+          SERVERLESS_INIT: "true"
+          ALPINE: ${{ matrix.arrays.isAlpine }}
+
+      - name: Set up build directory and copy binaries
+        run: cp -r .layers/. ./scripts/bin/
+
+      - name: Set up tracer installation script
+        run: cp ./scripts/serverless_init_dotnet.sh ./scripts/bin/
+
+      - name: Login to GHCR
+        uses: docker/login-action@b45d80f862d83dbcd57f89517bcf500b2ab88fb2 # v4.0.0
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Build and push
+        uses: docker/build-push-action@d08e5c354a6adb9ed34480a06d141179aa583294 # v7.0.0
+        with:
+          context: ./scripts
+          file: ./scripts/${{ matrix.arrays.dockerFile }}
+          push: true
+          tags: |
+            ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:latest-main${{ matrix.arrays.tagSuffix }}
+            ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:main-${{ steps.meta.outputs.stamp }}-${{ steps.meta.outputs.short_sha }}${{ matrix.arrays.tagSuffix }}
+          provenance: false
+          platforms: linux/amd64,linux/arm64
+
+  retry:
+    needs: [build-nightly]
+    if: failure() && fromJSON(github.run_attempt) < 2
+    runs-on: ubuntu-22.04
+    permissions:
+      actions: write
+    steps:
+      - name: Retry failed action
+        env:
+          GH_REPO: ${{ github.repository }}
+          GH_TOKEN: ${{ github.token }}
+        run: gh workflow run retry-workflow.yml -F run_id=${{ github.run_id }}
+
+  notify:
+    needs: [build-nightly]
+    if: failure() && fromJSON(github.run_attempt) >= 2
+    runs-on: ubuntu-22.04
+    steps:
+      - name: Notify Slack
+        env:
+          SLACK_CHANNEL: "#serverless-agent"
+          SLACK_WEBHOOK: ${{ secrets.SLACK_WEBHOOK }}
+        run: |
+          OPS_MESSAGE=":gh-check-failed: Nightly serverless-init build failed!
+
+          The nightly build from datadog-agent main did not succeed after retry.
+
+          See ${GITHUB_SERVER_URL}/${GITHUB_REPOSITORY}/actions/runs/${GITHUB_RUN_ID} for details."
+
+          curl -H "Content-type: application/json" -X POST "$SLACK_WEBHOOK" \
+            -d "$(jq -n --arg channel "$SLACK_CHANNEL" --arg text "$OPS_MESSAGE" '{channel: $channel, text: $text}')"