ci: support manual release tag for image publish

.github/workflows/release-image.yml

@@ -8,6 +8,11 @@ on:
     tags:
       - "v*"
   workflow_dispatch:
+    inputs:
+      release_tag:
+        description: "Release tag to publish (for example v0.2.0). Optional."
+        required: false
+        type: string
 
 permissions:
   contents: read
@@ -41,6 +46,7 @@ jobs:
           images: ghcr.io/${{ github.repository }}
           tags: |
             type=ref,event=tag
+            type=raw,value=${{ github.event.inputs.release_tag }},enable=${{ github.event_name == 'workflow_dispatch' && github.event.inputs.release_tag != '' }}
             type=raw,value=latest
 
       - name: Build and push