vtorc: rename isClusterWideRecovery -> isShardWideRecovery

[timvaillancourt]

Description

This PR renames the VTOrc term "cluster-wide" to "shard-wide" for clarity

Referring to a shard as a "cluster" seems to be a byproduct of old-Orchestrator, which referred to "groups" of instances as "clusters" (and shards would be a "cluster")

In Vitess, a "cluster" typically refers to all keyspaces/shards/vtgates/topo, which makes the terminology (to me) at-odds

Related Issue(s)

Checklist

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

Deployment Notes

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[codecov]

Codecov Report

Attention: Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.

Project coverage is 67.49%. Comparing base (2520f7f) to head (8f4ebb1).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/vtorc/logic/topology_recovery.go	0.00%	5 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #18351   +/-   ##
=======================================
  Coverage   67.49%   67.49%           
=======================================
  Files        1603     1603           
  Lines      262428   262441   +13     
=======================================
+ Hits       177114   177126   +12     
- Misses      85314    85315    +1     

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