fedora-common-ostree: Workaround for SAMBA support in cups

RPM %triggerin are not currently supported in rpm-ostree, thus work
around this issue by manually creating the symlink.

According to the docs, `/usr/lib/cups/backend/smb` should point to `smbspool`.
Here we have the following chain:

/usr/lib/cups/backend/smb -> /usr/libexec/samba/cups_backend_smb -> /etc/alternatives/cups_backend_smb -> /usr/bin/smbspool

See: https://www.cups.org/blog/2005-06-17-printing-to-windows-servers-with-samba.html
See: coreos/rpm-ostree#1180
See: fedora-silverblue/issue-tracker#532

fedora-common-ostree.yaml

@@ -138,4 +138,8 @@ postprocess:
     rm -rf /etc/systemd/user/*
     systemctl --user --global preset-all
 
+    # Fix triggerin for samba-client in cups package (not supported by rpm-ostree yet)
+    # https://github.com/fedora-silverblue/issue-tracker/issues/532
+    ln -snf /usr/libexec/samba/cups_backend_smb /usr/lib/cups/backend/smb
+
 postprocess-script: "postprocess.sh"