IPU 9 -> 10: obsolete GPG key with SHA1 signature

When upgrading to RHEL 10, we have analogical problem as we had for
IPU 8 -> 9 due to GPG keys with SHA1 signatures. The SHA1 algorithm
is considered unsecure since RHEL 9 and all RPMs are required to be
signed by keys with SHA2 signatures. The RHEL 9 GPG (auxiliary) key
is unfortunately still signed with SHA1 and RHEL 10 tooling refuse
to use it for any operations.

To resolve this apply the same solution as we did in the past:
* obsolete original key
* install the target RHEL 10 GPG keys during the upgrade

repos/system_upgrade/common/files/distro/rhel/gpg-signatures.json

@@ -14,6 +14,6 @@
             "gpg-pubkey-db42a60e-37ea5438"
           ],
         "9": ["gpg-pubkey-d4082792-5b32db75"],
-        "10": []
+        "10": ["gpg-pubkey-fd431d51-4ae0493b"]
     }
 }