Add flake finder periodic E2E tests

Periodically run E2E tests against the merged (must have passed E2E
gating) code to detect breakages due to external changes or flaky
failures.

Also supports debugging Helm-related failures in other repositories, by
verifying (or not) what's passing here.

Use the same test matrix as the current E2E job.

Mirrors similar tests in other Submariner repositories.

Signed-off-by: Daniel Farrell <dfarrell@redhat.com>

.github/workflows/flake_finder.yml

@@ -0,0 +1,30 @@
+---
+name: Flake Finder
+
+on:
+  schedule:
+    - cron: "0 0 * * *"
+
+jobs:
+  e2e:
+    name: E2E
+    timeout-minutes: 30
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        cable_driver: ['libreswan', 'wireguard']
+        globalnet: ['', 'globalnet']
+        lighthouse: ['', 'lighthouse']
+    steps:
+      - name: Check out the repository
+        uses: actions/checkout@v2
+
+      - name: Run E2E deployment and tests
+        uses: submariner-io/shipyard/gh-actions/e2e@devel
+        with:
+          using: ${{ matrix.cable_driver }} ${{ matrix.globalnet }} ${{ matrix.lighthouse }}
+
+      - name: Post mortem
+        if: failure()
+        uses: submariner-io/shipyard/gh-actions/post-mortem@devel