[infrastructure] Certify the signal UBI image on release

The signal UBI image is published with every release, but only images
listed in the certification workflow reach the Red Hat catalog, so it
would otherwise need a manual run each time.

Add signal to the dispatch options and the component list, using the
same -ubi tag suffix as .goreleaser.yaml. The run reads its Partner
Connect ID from REDHAT_CERT_ID_SIGNAL.

.github/workflows/redhat-certify.yml

@@ -33,6 +33,7 @@ on:
           - client-rootless
           - reverse-proxy
           - netbird-server
+          - signal
       version:
         description: "Released version, e.g. v0.80.0"
         type: string
@@ -68,6 +69,7 @@ jobs:
             "client-rootless ghcr.io/netbirdio/netbird -rootless-ubi"
             "reverse-proxy ghcr.io/netbirdio/reverse-proxy -ubi"
             "netbird-server ghcr.io/netbirdio/netbird-server -ubi"
+            "signal ghcr.io/netbirdio/signal -ubi"
           )
           matrix="[]"
           missing=()