add hostname to backup manifest

[rvrangel]

Description

This PR adds the hostname of the host taking the backup to the BackupManifest to make it easier to identify and filter backups with that information as well.

Related Issue(s)

• Feature Request: Add Hostname to the BackupManifest #18846

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

[vitess-bot]

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[rvrangel]

the mysqlshell engine is the only one we have unit tests for ExecuteBackup, so I only verified this here

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.70%. Comparing base (1cfedac) to head (cd410cf).
⚠️ Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/mysqlctl/xtrabackupengine.go	0.00%	4 Missing ⚠️
go/vt/mysqlctl/builtinbackupengine.go	75.00%	1 Missing ⚠️
go/vt/mysqlctl/mysqlshellbackupengine.go	75.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #18847   +/-   ##
=======================================
  Coverage   69.70%   69.70%           
=======================================
  Files        1607     1607           
  Lines      214579   214620   +41     
=======================================
+ Hits       149572   149605   +33     
- Misses      65007    65015    +8     

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[timvaillancourt]

Makes sense to me 👍

[dbussink]

We also have netutil.FullyQualifiedHostname, should that be used instead?

[rvrangel]

ah cool, I didn't know we had that, I have updated the PR