Update e2e-test workflow

Author: sawantpritam

.github/workflows/e2e.yml

@@ -15,15 +15,29 @@
 name: Build e2e tests
 
 on:
-  workflow_run:
-    workflows:
-      - Trigger build
-    types:
-      - completed
+  push:
+    branches: [ develop ]
+  pull_request:
+      branches: [ develop ]
+      types: [ opened, synchronize, reopened, labeled ]
+  workflow_dispatch:
 
 jobs:
   build:
     runs-on: k8s-runner-e2e
+    # We allow builds:
+    # 1) When triggered manually
+    # 2) When it's a merge into a branch
+    # 3) For PRs that are labeled as build and
+    #  - It's a code change
+    #  - A build label was just added
+    # A bit complex, but prevents builds when other labels are manipulated
+    if: >
+      github.event_name == 'workflow_dispatch'
+      || github.event_name == 'push'
+      || (contains(github.event.pull_request.labels.*.name, 'build')
+          && (github.event.action != 'labeled' || github.event.label.name == 'build')
+          )
     strategy:
       matrix:
         module: [mysql-plugin, postgresql-plugin]