IPA: validate conflicts with other installers, return proper error

[mna]

Related issue: Resolves #36621

Checklist for submitter

• Changes file added for user-visible changes in changes/, orbit/changes/ or ee/fleetd-chrome/changes.
  See Changes files for more information.

• Input data is properly validated, SELECT * is avoided, SQL injection is prevented (using placeholders for values in statements)

Testing

• Added/updated automated tests

• Where appropriate, automated tests simulate multiple hosts and test for host isolation (updates to one hosts's records do not affect another)

• QA'd all new/changed functionality manually

[codecov]

Codecov Report

❌ Patch coverage is 43.63636% with 93 lines in your changes missing coverage. Please review.
✅ Project coverage is 62.23%. Comparing base (3cf50f8) to head (025bac2).

Files with missing lines	Patch %	Lines
server/datastore/mysql/in_house_apps.go	56.25%	29 Missing and 6 partials ⚠️
server/datastore/mysql/software_installers.go	35.71%	16 Missing and 11 partials ⚠️
server/datastore/mysql/vpp.go	40.00%	11 Missing and 7 partials ⚠️
ee/server/service/vpp.go	0.00%	13 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #38005      +/-   ##
==========================================
- Coverage   65.88%   62.23%   -3.66%     
==========================================
  Files        2393     2393              
  Lines      191036   191170     +134     
  Branches     8484     8484              
==========================================
- Hits       125872   118980    -6892     
- Misses      53726    61314    +7588     
+ Partials    11438    10876     -562     

Flag	Coverage Δ
backend	63.49% <43.63%> (-4.23%)	⬇️

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