a new model operator secret is created whenever controller restarts

[Yang Kelvin Liu]

I deleted controller pods a few times for restarting the controller, then I got lots of model operator secrets created.

```console
# delete controller pod a few times:
$ mkubectl -ncontroller-k1 delete pod/controller-0

$ mkubectl -ncontroller-k1 get secrets -o json | jq '.items[] | select(.metadata.annotations["kubernetes.io/service-account.name"]=="modeloperator") | .metadata.name'
"modeloperator-token-2c29m"
"modeloperator-token-vlc7j"
"modeloperator-token-zs2nx"
"modeloperator-token-d9jv2"
"modeloperator-token-784s7"
"modeloperator-token-nnt4s"
"modeloperator-token-7dkhr"
"modeloperator-token-m9t9f"
"modeloperator-token-gtxrd"
"modeloperator-token-gjn24"
"modeloperator-token-rmz94"
"modeloperator-token-q59s6"
"modeloperator-token-vkgc8"
"modeloperator-token-nwwrx"
"modeloperator-token-v528n"
"modeloperator-token-fdzt8"
"modeloperator-token-m89jr"
"modeloperator-token-2spnz"

```

[Canonical Juju QA Bot (juju-qa-bot)]

This Medium-priority bug has not been updated in 60 days, so we're marking it Low importance. If you believe this is incorrect, please update the importance.