add imageid output and use metadata to set digest output

Signed-off-by: CrazyMax <crazy-max@users.noreply.github.com>

action.yml

@@ -89,8 +89,10 @@ inputs:
     required: false
 
 outputs:
+  imageid:
+    description: 'Image ID'
   digest:
-    description: 'Image content-addressable identifier also called a digest'
+    description: 'Image digest'
   metadata:
     description: 'Build result metadata'