Allow for passing in optional branch name to workflow_dispatch build

Signed-off-by: Adam Warner <me@adamwarner.co.uk>

.github/workflows/workflow_dispatch.yml

@@ -2,6 +2,10 @@ name: Build & Deploy custom image manually
 on:
   workflow_dispatch:
     inputs:
+      branch:
+        description: "Name of Branch to base build on"
+        required: false
+        default: dev
       name:
         description: 'Name of tag'
         required: true
@@ -30,7 +34,7 @@ jobs:
       - name: Checkout Repo
         uses: actions/checkout@v2
         with:
-          ref: dev
+          ref: ${{ github.event.inputs.branch }}
       - name: Patching Versions File
         run: |
           git checkout -b ${{ github.event.inputs.name }}