VTGate/foreign keys stress test: add tests for 'standard' replica

[shlomi-noach]

Description

#13799 introduced VTGate stress tests for foreign keys, and #14098 further improved them. Among the techniques used, we set up a primary with foreign key tables, and a replica where we stripped out the foreign key constraints. This setup validated that VTGate's cascading of foreign key rules works correctly, by comparing data on primary and replica.

This PR adds an additional replica, this time a standard, "faithful" one. The objective with this replica is to validate that the schema on primary and replica are consistent after Online DDL. This is something we can't do with the already existing replica as we intentionally diverged the schema on that replica in the first place.

The test compares the new, "faithful" replica with the primary, expected identical schema, explicitly makes sure that foreign key referenced tables are pinned to the correct primaries (validating the effects of rename_table_preserve_foreign_key) and of course also validates that the data is identical.

We are modifying the behavior of rename_table_preserve_foreign_key in our public fork. The tests are expected to fail right away and to pass once we've updated the forked MySQL image pass as we're not yet using the forked MySQL image in this repo's CI.

Related Issue(s)

#11975

Checklist

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

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[shlomi-noach]

Looking for 2nd review.