[release-16.0] Upgrade-Downgrade Fix: Schema-initialization stuck on semi-sync ACKs while upgrading (#13411)

[GuptaManan100]

Description

This PR is a backport of #13411.

When we introduced the schema-init-db code, we failed to realize that it would start doing writes as part of the code to change the tablet type. As part of the PRS process, we used to call PromoteReplica first, followed by calls to SetReplicationSource.

When a user upgrades from v16 (/v15) to v17 (/v16), as part of PromoteReplica call, the schema-init realizes that there are schema diffs to apply and ends up writing to the database. The problem is that if semi-sync is enabled, all of these writes get blocked indefinitely. Eventually, PromoteReplica fails and this fails the entire PRS call.

In this PR we fix this issue, by altering the PRS flow slightly, where we call SetReplicationSource on all the replicas and PromoteReplica on the new primary in parallel. This allows PromoteReplica to be unblocked just as any semi-sync capable replica reparents to it.

As part of this PR, the upgrade-downgrade tests for manual backups has been augmented as well to start using semi-sync and to follow the correct steps to upgrade the cluser instead of just shutting down all the tablets and restarting all the tablets. Also, we call PlannedReparentShard now in the test instead of InitShardPrimary which has been long deprecated.

Related Issue(s)

• Fixes Bug Report: upgrade to v16 from v15 blocks on semi-sync #13426

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

Deployment Notes

[vitess-bot]

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