In #8435 (shipped in 0.12.1), we updated the `Job.Register` RPC to atomically
write the eval along with the job. But this didn't get copied to
`Job.Dispatch`. Under excessive load testing we demonstrated this can result in
dispatched jobs without corresponding evals.
Update the dispatch RPC to write the eval in the same Raft log as the job
registration. Note that we don't need to version-check this change for upgrades,
because the register and dispatch RPCs share the same `JobRegisterRequestType`
Raft message, and therefore all supported server versions already look for the
eval in the FSM. If an updated leader includes the eval, older followers will
write the eval. If a non-updated leader writes the eval in a separate Raft
entry, updated followers will write those evals normally.
Fixes: https://github.com/hashicorp/nomad/issues/26655
Ref: https://hashicorp.atlassian.net/browse/NMD-947
Ref: https://github.com/hashicorp/nomad/pull/8435
