MoveTables: confirm tables are loaded into vttablet schema engine cache before starting workflow

[rohit-nayak-ps]

Description

There is a race between the creation of the schema in MoveTables and the reloading of the schema in vttablet which results in some tables not being visible to the workflow when it starts up. It was surfaced by #13178.

This PR adds an additional check after creating the new tables on the target. It validates that the tablet schema cache has the new tables before starting the workflows.

Related Issue(s)

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

[vitess-bot]

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[dbussink]

I don't think we need this, I found the issue with #13178 and fixed that.