vtorc: add cell/location context

[timvaillancourt]

Description

This PR adds to VTOrc the knowledge of what Vitess Cell a VTOrc process is running within. This knowledge will be used to gain confidence in certain VTOrc problems, by asking another cell to validate the detected problem

Today some problems (example vttablet down on PRIMARY) are not actioned by VTOrc, because it does not have enough confidence in it's detection from a single angle. On the opposite extreme, sometimes VTOrc believes it is correct using limited details, from only it's perspective

The topology recovery side of this change will come in future PRs, for now having this in v24 will be useful

Details:

• --cell flag added to VTOrc
  • This flag will become required (like vtgate) in v25+
  • If defined, the cell is validated using the topo
    • Currently the new-flag value is not used in any VTOrc logic. The goal here was to just introduce the flag
  • If undefined, an error warning this flag will be required in v25+ is logged
• 100+ end-to-end tests updated for new .StartVTOrc/.StartVTOrcs/etc signature (😞)
• examples/ shell scripts updated for new flag

Related Issue(s)

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

Deployment Notes

AI Disclosure

[codecov]

Codecov Report

❌ Patch coverage is 0% with 23 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.90%. Comparing base (749fe54) to head (dfb84d1).
⚠️ Report is 14 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/vtorc/server/discovery.go	0.00%	15 Missing ⚠️
go/vt/vtorc/config/config.go	0.00%	4 Missing ⚠️
go/cmd/vtorc/cli/cli.go	0.00%	3 Missing ⚠️
go/cmd/vtgate/cli/cli.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #19047      +/-   ##
==========================================
+ Coverage   69.88%   69.90%   +0.02%     
==========================================
  Files        1610     1612       +2     
  Lines      215431   215815     +384     
==========================================
+ Hits       150551   150863     +312     
- Misses      64880    64952      +72     

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[timvaillancourt]

Fix for flakiness. 1 or more is fine for this test - the important part is the ERS gets skipped

[promptless]

📝 Documentation updates detected!

New suggestion: Document VTOrc --cell flag

[timvaillancourt]

Unrelated change to make it clear to users that VTGate requires this flag

[promptless]

📝 Documentation updates detected!

New suggestion: Add changelog entry for VTOrc --cell flag