tech: use a Github Action to trigger CircleCI

This will let us trigger build-and-test workflow
on pull request only

See https://circleci.com/blog/trigger-circleci-pipeline-github-action/

.circleci/config.yml

@@ -21,6 +21,20 @@
 
 version: 2.1
 
+parameters:
+  GHA_Actor:
+    type: string
+    default: ''
+  GHA_Action:
+    type: string
+    default: ''
+  GHA_Event:
+    type: string
+    default: ''
+  GHA_Meta:
+    type: string
+    default: ''
+
 orbs:
   browser-tools: circleci/[email protected]
 
@@ -93,6 +107,10 @@ executors:
 workflows:
   version: 2
   build-and-test:
+    # This workflow is set to be conditionally triggered, only when
+    # the GitHub Action is triggered.
+    # With no other workflows, normal push events will be ignored currently.
+    when: << pipeline.parameters.GHA_Action >>
     jobs:
       - checkout:
           context: Pix

.github/workflows/trigger-ci.yaml

@@ -0,0 +1,19 @@
+name: Trigger CircleCI
+
+on:
+  pull_request:
+    types: [opened, reopened, synchronize, ready_for_review]
+  push:
+    branches: dev
+
+jobs:
+  trigger-ci:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Trigger CircleCI
+        # ensure PR is not draft
+        if: '! github.event.pull_request.draft'
+        uses: CircleCI-Public/[email protected]
+        env:
+          CCI_TOKEN: ${{ secrets.GUL_TEST_TRIGGER_CIIRCLECI_TOKEN }}