Replace temp triggers with workflow dispatch

Author: matthewelwell

.github/workflows/platform-docker-build-e2e-image.yml

@@ -1,13 +1,10 @@
 name: Build E2E Frontend Base Image
 
 on:
-  push:
-    paths:
-      - frontend/Dockerfile-base.e2e
-      - .github/workflows/platform-docker-build-e2e-image.yml
   schedule:
     # Update the E2E Firefox testcafe version on the first of every month
     - cron: 0 0 1 * *
+  workflow_dispatch:
 
 jobs:
   build-e2e-docker-image: