Fix permissions of update-gradle-wrapper and add workflow_dispatch

Author: adwsingh

.github/workflows/update-gradle-wrapper.yml

@@ -1,12 +1,14 @@
 permissions:
-  contents: read
+  contents: write
+  pull-requests: write
 name: Update Gradle Wrapper
 # Needed because dependabot doesn't support updating the gradle wrapper
 # see: https://github.com/dependabot/dependabot-core/issues/2223
 
 on:
   schedule:
     - cron: "0 14 * * 1" # 2PM UTC (7AM PST) every Monday.
+  workflow_dispatch:
 
 jobs:
   update-gradle-wrapper: