Add scheduled workflow to trigger snapshot releases.

.github/workflows/schedule_snapshot_release.yml

diff --git a/.github/workflows/schedule_snapshot_release.yml b/.github/workflows/schedule_snapshot_release.yml
new file mode 100644
index 0000000..32d93bd
--- /dev/null
+++ b/.github/workflows/schedule_snapshot_release.yml
@@ -0,0 +1,57 @@
+name: Schedule snapshot release
+
+on:
+  schedule:
+    - cron:  '0 10,22 * * *'
+
+  workflow_dispatch:
+
+jobs:
+  tag_release:
+    name: "Tag snapshot release"
+    runs-on: ubuntu-18.04
+    steps:
+      - name: Checking out repository
+        uses: actions/checkout@v2
+        with:
+          token: ${{ secrets.GITHUB_WRITE_ACCESS_TOKEN }}
+
+      - name: Compute version
+        run: |
+          git fetch --depth=1 origin +refs/tags/*:refs/tags/*
+          package_version="$(printf '%(%Y%m%d)T.${{ github.run_number }}')"
+          tag_name="snapshot-${package_version}"
+          echo "package_version=${package_version}" >> $GITHUB_ENV
+          echo "tag_name=${tag_name}" >> $GITHUB_ENV
+
+      - name: Updating snapshot tag
+        run: |
+          git tag "${tag_name}"
+
+      - name: Pushing changes
+        uses: ad-m/github-push-action@v0.6.0
+        with:
+          github_token: ${{ secrets.GITHUB_WRITE_ACCESS_TOKEN }}
+          branch: main
+          tags: true
+
+      - name: Create Release
+        id: create_release
+        uses: actions/create-release@v1
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_WRITE_ACCESS_TOKEN }}
+        with:
+          tag_name: ${{ env.tag_name }}
+          release_name: iree snapshot ${{ env.tag_name }}
+          body: |
+            Automatic snapshot release of iree.
+          draft: true
+          prerelease: true
+
+      - name: "Invoke workflow :: Build Native Release Packages"
+        uses: benc-uk/workflow-dispatch@v1
+        with:
+          workflow: Build Native Release Packages
+          token: ${{ secrets.WRITE_ACCESS_TOKEN }}
+          ref: "${{ env.tag_name }}"
+          inputs: '{"package_suffix": "-snapshot", "package_version": "${{ env.package_version }}", "release_id": "${{ steps.create_release.outputs.id }}"}'