Atomic Transactions correctness with PRS, ERS and MySQL & Vttablet Restarts

[GuptaManan100]

Description

This PR makes the code changes required to ensure that atomic transactions don't break their atomic guarantee in the face of disruptions like PlannedReparentShard, EmergencyReparentShard, and MySQL and Vttablet restarts.

A lot of the logic on how we redo the prepared transactions had to be reworked. This PR also adds the design docs for these changes so that they can referenced in the future too.

The testing strategy for ensuring these changes work as intended is 2-fold -

1. Fuzzer testing to randomly run disuptions in the fuzzer we previously added, which still ensures in the end that all accepted writes must be atomic.
2. Explicit stress testing, that leverages our ability to write debug-only code into the binaries that we use for testing. We explicitly make the CommitPrepared stall on one of the shards, and then run a disruption to ensure that that write still gets committed without any other write on the same row going through.

This PR also adds a new design doc explaining all the steps that are involved in guaranteeing that atomic transactions work well with each of the many disruptions

Related Issue(s)

• RFC: Atomic Distributed Transactions #16245

Checklist

• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

Deployment Notes

[vitess-bot]

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[harshit-gangal]

Overall looking good.