Add definition of new action input (llm-d#123)

Signed-off-by: Shmuel Kallner <kallner@il.ibm.com>
Signed-off-by: Sergey Marunich <marunich.s@gmail.com>

Author: shmuelk

.github/actions/docker-build-and-push/action.yml

@@ -13,6 +13,10 @@ inputs:
   registry:
     required: true
     description: Container registry (e.g., ghcr.io/llm-d)
+  prerelease:
+    required: true
+    description: indicates whether or not this is a pre-release (not a release) build
+
 runs:
   using: "composite"
   steps: