Cherry-pick: Improved validation for host transfers (#40345)

[nulmete]

Testing

• Added/updated automated tests

• QA'd all new/changed functionality manually

[codecov]

Codecov Report

❌ Patch coverage is 90.90909% with 2 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (rc-minor-fleet-v4.82.0@f2ec746). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
server/service/hosts.go	90.90%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@                    Coverage Diff                    @@
##             rc-minor-fleet-v4.82.0   #40409   +/-   ##
=========================================================
  Coverage                          ?   66.37%           
=========================================================
  Files                             ?     2456           
  Lines                             ?   196784           
  Branches                          ?     8577           
=========================================================
  Hits                              ?   130620           
  Misses                            ?    54350           
  Partials                          ?    11814           

Flag	Coverage Δ
backend	68.14% <90.90%> (?)

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