Fix error when updating a cluster that already has JobSet (#622)

Recently, `cluster create-pathways` has been failing with a conflict
while installing JobSet on pre-existing clusters. This change adds
`--force-conflicts` which resolves the issue.

Author: lukebaumann

src/xpk/core/cluster.py

@@ -62,8 +62,8 @@ def set_jobset_on_cluster(args) -> int:
     0 if successful and 1 otherwise.
   """
   command = (
-      'kubectl apply --server-side -f'
-      f' https://github.com/kubernetes-sigs/jobset/releases/download/{JOBSET_VERSION}/manifests.yaml'
+      'kubectl apply --server-side --force-conflicts'
+      f' -f https://github.com/kubernetes-sigs/jobset/releases/download/{JOBSET_VERSION}/manifests.yaml'
   )
   task = f'Install Jobset on {args.cluster}'
   return_code = run_command_with_updates_retry(command, task, args)