test: add GitHub action for end-to-end tests (#5452)

Partial fix for #5291.

.github/workflows/e2e.yml

@@ -0,0 +1,38 @@
+name: e2e-tests
+# Runs the CI end-to-end test network on all pushes to master or release branches
+# and every pull request, but only if any Go files have been changed.
+on:
+  pull_request:
+  push:
+    branches:
+      - master
+      - release/**
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    timeout-minutes: 15
+    steps:
+      - uses: actions/checkout@v2
+      - uses: technote-space/get-diff-action@v3
+        with:
+          SUFFIX_FILTER: |
+            .go
+            .mod
+            .sum
+          SET_ENV_NAME_INSERTIONS: 1
+          SET_ENV_NAME_LINES: 1
+
+      - name: Build
+        working-directory: test/e2e
+        # Run two make jobs in parallel, since we can't run steps in parallel.
+        run: make -j2 docker runner
+
+      - name: Run CI testnet
+        working-directory: test/e2e
+        run: sudo ./build/runner -f networks/ci.toml
+
+      - name: Emit logs on failure
+        if: ${{ failure() }}
+        working-directory: test/e2e
+        run: ./build/runner -f networks/ci.toml logs