examples: fix flag syntax for zkctl

[deepthi]

Description

Running the local example with TOPO=zk2 fails with an error from zkctl startup.
This is because we changed flags to use -- instead of - back in v16.
This was broken at least on main, most likely on 17, and probably on v16 as well.

Related Issue(s)

Fixes #14471

Checklist

• "Backport to:" labels have been added if this change should be back-ported
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on the CI
• Documentation was added or is not required

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[deepthi]

We don't seem to run local example with zookeeper in CI. If we did, we might have caught this.
OTOH, we still have this, though we've deleted the k8s topo. I'm not sure how that is passing.

local_example / Local example using k8s on ubuntu-22.04 (pull_request) 

[dbussink]

OTOH, we still have this, though we've deleted the k8s topo. I'm not sure how that is passing.

Code looks like this:

# start topo server
if [ "${TOPO}" = "zk2" ]; then
  CELL=zone1 ../common/scripts/zk-up.sh
elif [ "${TOPO}" = "consul" ]; then
  CELL=zone1 ../common/scripts/consul-up.sh
else
  CELL=zone1 ../common/scripts/etcd-up.sh
fi

So it considers the default to be etcd, if you set something random / unknown.

[mattlord]

Ah, that’s why we didn’t notice 🙂

[mattlord]

I removed the local k8s example from the required checks for main.

[mattlord]

Maybe we want to make the zk2 one required? Wasn’t sure about that.