Add temporary beta pipeline workflow

Author: coreycb

.github/workflows/beta-pipeline.yml

@@ -0,0 +1,21 @@
+name: Beta Pipeline
+
+on:
+  workflow_dispatch:
+    inputs:
+      version:
+        description: 'Version to build'
+        required: false
+        type: string
+      notify_testers:
+        description: 'Notify external testers'
+        required: false
+        default: true
+        type: boolean
+
+jobs:
+  call-shippable-builds:
+    uses: coreycb/thunderbird-ios/.github/workflows/shippable-builds.yml@beta
+    with:
+      version: ${{ github.event.inputs.version }}
+      notify_testers: ${{ github.event.inputs.notify_testers }}