upgrade RKE2 > 1.28.8

We currently are stuck on RKE2 1.28.8 because of #1347 (closed) (upstream https://github.com/rancher/rke2/issues/6208).

Because of this we are subject to some known RKE2 bugs that are solved in more recent releases:

• #1157 (closed)
• #1421 (closed)

We need to:

• solve #1347 (closed)
• then upgrade RKE2
• then do cleanups (in particular #1425 (closed))