VReplication: Auto renew lease on Keyspace Lock

[mattlord]

Description

VReplication uses Keyspace topo server locks in order to prevent concurrent changes that could cause breakages. It does that in these primary locations:

1. When performing a traffic switch (SwitchTraffic and ReverseTraffic) in various workflows like MoveTables and Reshard
2. When cleaning up resources related to a workflow when canceling/deleting/completing it
3. When initializing a VDiff

This is done in order to prevent concurrent changes to shared resources such as the _vt.vreplication record on target shards.

At some point, I think we should add a distributed workflow lock in the topo to coordinate on related issues. We may want those both at a keyspace level and at a shard level — depending on the level of concurrency control we require for the given operation. This lock can then also be held for as long as needed as it would not impact other Vitess operations (the Keyspace Lock is used for things e.g. like updating the throttler config, durability policy, or schema for a keyspace). This will be a major project, however, and for the time being we can instead make a relatively minor change to how the Keyspace locks are managed in the noted cases within VReplication. In this PR the change is that we automatically renew the Keyspace Lock while holding it, up to a maximum time (hard coded at 10 mins now but will probably add a flag for this ~ --max-keyspace-lock-ttl=<duration> which defaults to 10m).

Related Issue(s)

• Fixes: Bug Report: VDiff2 topo keyspace locks can be released too early #11811

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• 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

[vitess-bot]

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[mattlord]

This is unrelated, but addresses a panic raised in the Vitess Slack where the target shard had no primary tablet.

[codecov]

Codecov Report

Attention: Patch coverage is 31.71806% with 155 lines in your changes missing coverage. Please review.

Project coverage is 68.56%. Comparing base (7a737f4) to head (9f9f13f).
Report is 2 commits behind head on main.

Files	Patch %	Lines
go/vt/vtctl/workflow/server.go	31.44%	109 Missing ⚠️
go/vt/vttablet/tabletmanager/vdiff/table_differ.go	0.00%	31 Missing ⚠️
go/vt/topo/keyspace_lock.go	58.06%	13 Missing ⚠️
go/vt/vtctl/workflow/resharder.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16240      +/-   ##
==========================================
- Coverage   68.61%   68.56%   -0.06%     
==========================================
  Files        1544     1544              
  Lines      197993   198176     +183     
==========================================
+ Hits       135848   135874      +26     
- Misses      62145    62302     +157     

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[mattlord]

Replaced by: #16260