Move from TravisCI to GitHub Actions

This moves the CI configuration from TravisCI, which we're no longer using
after their disasterous response to a huge security vulnerability, to GitHub
Actions.

It uses a templated GitHub Actions workflow file, which should be mostly
identical between all repositories.

Along the way some other nice goodies are included:
- Run all tests against Node.js 12, 14, and 16
- Run docker build _after_ any NPM publish, so that versioned docker images can be built
- Remove any CircleCI config that exists (we can use Github Actions to build docker images just fine)
- Remove any other lingering references to TravisCI

.github/workflows/push.yml

@@ -39,3 +39,21 @@ jobs:
           if [[ -n "$GH_TOKEN" && -n "$NPM_TOKEN" ]]; then
             curl "https://raw.githubusercontent.com/pelias/ci-tools/master/semantic-release.sh" | bash -
           fi
+  build-docker-images:
+    # run this job if the unit tests passed and the npm-publish job was a success or was skipped
+    # note: github actions won't run a job if you don't call one of the status check functions, so `always()` is called since it evalutes to `true`
+    if: ${{ always() && needs.unit-tests.result == 'success' && (needs.npm-publish.result == 'success' || needs.npm-publish.result == 'skipped') }}
+    needs: [unit-tests, npm-publish]
+    runs-on: ubuntu-20.04
+    steps:
+      - uses: actions/checkout@v2
+      - name: Dump needs context
+        env:
+          NEEDS_CONTEXT: ${{ toJSON(needs) }}
+        run: echo "$NEEDS_CONTEXT"
+      - name: Build Docker images
+        env:
+          DOCKER_USERNAME: ${{ secrets.DOCKER_USERNAME }}
+          DOCKER_PASSWORD: ${{ secrets.DOCKER_PASSWORD }}
+        run: |
+          curl "https://raw.githubusercontent.com/pelias/ci-tools/master/build-docker-images.sh" | bash -