Website: Make manual build ref configurable

Author: zefhemel

.github/workflows/docker-website.yml

@@ -11,6 +11,11 @@ on:
         options:
           - edge
           - latest
+      git_ref:
+        description: "Git tag/branch to checkout for website content"
+        required: true
+        default: "main"
+        type: string
       base_image:
         description: "Base SilverBullet image (e.g. zefhemel/silverbullet:v2)"
         required: true
@@ -26,6 +31,8 @@ jobs:
     steps:
       - name: Setup repo
         uses: actions/checkout@v3
+        with:
+          ref: ${{ inputs.git_ref }}
 
       - name: Login to Docker Hub
         uses: docker/login-action@v2