[self-hosted] Add a UBI image variant for the combined server (#7953)

* [self-hosted] Add a UBI image variant for the combined server

OpenShift and other Red Hat environments expect UBI-based images that run
as an arbitrary non-root UID. The proxy and rootless client already ship
-ubi variants; this adds the same for netbird-server, published as
<version>-ubi and ubi-latest for amd64 and arm64.

* [self-hosted] Check the license output path before creating temp files

The existing-output exit ran before the cleanup trap was registered, so it
left the two mktemp files behind.

* [self-hosted] Certify the netbird-server UBI image

Adds netbird-server to the Red Hat certification components. Its Partner
Connect component ID goes in the REDHAT_CERT_ID_NETBIRD_SERVER repository
variable.

.github/workflows/redhat-certify.yml

@@ -32,6 +32,7 @@ on:
           - all
           - client-rootless
           - reverse-proxy
+          - netbird-server
       version:
         description: "Released version, e.g. v0.80.0"
         type: string
@@ -66,6 +67,7 @@ jobs:
           components=(
             "client-rootless ghcr.io/netbirdio/netbird -rootless-ubi"
             "reverse-proxy ghcr.io/netbirdio/reverse-proxy -ubi"
+            "netbird-server ghcr.io/netbirdio/netbird-server -ubi"
           )
           matrix="[]"
           missing=()