chore: use anonymous func to generate tags and add tests

Signed-off-by: CrazyMax <1951866+crazy-max@users.noreply.github.com>

action.yml

@@ -13,7 +13,7 @@ inputs:
     required: true
   images:
     description: 'List of Docker images to use as base name for tags'
-    required: true
+    required: false
   tags:
     description: 'List of tags as key-value pair attributes'
     required: false