examples: Fix Vtop example and release script

[deepthi]

Description

Since the default images are now MySQL 8.0, we need to update the operator example to use the right property for the image.

This PR also fixes the image we use for vtadmin deployment and fixes the release script to also change that automatically.
Further the vtop example script is fixed to use vtctldclient inplace of vtctlclient.

Related Issue(s)

Fixes #12438

Checklist

• "Backport to:" labels have been added if this change should be back-ported
• Tests were added or are not required
• Documentation was added or is not required

Deployment Notes

[vitess-bot]

Review Checklist

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[deepthi]

I noticed that vtadmin image still has latest. Did we not build an rc1 image for it?

[deepthi]

This needs to be fixed on main as well, but I doubt the bot can do it. It will need a hand-crafted PR.

[vitess-bot]

I was unable to forwardport this Pull Request to the following branches: main.