move PhoneNumberAlreadyInUse to verification_service.go

[MatousJobanek]

• moves the PhoneNumberAlreadyInUse method into verification_service.go (it's used only there)
• transforms it into a standalone function
• moves & improves the unit tests

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: alexeykazakov, MatousJobanek, xcoulon

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• OWNERS [MatousJobanek,alexeykazakov,xcoulon]

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[alexeykazakov]

/retest

[sonarqubecloud]

Quality Gate passed

Issues
3 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

Attention: Patch coverage is 90.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 85.34%. Comparing base (28e6445) to head (e337618).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
pkg/verification/service/verification_service.go	90.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #504      +/-   ##
==========================================
+ Coverage   85.11%   85.34%   +0.22%     
==========================================
  Files          32       32              
  Lines        3118     3118              
==========================================
+ Hits         2654     2661       +7     
+ Misses        376      371       -5     
+ Partials       88       86       -2     

Flag	Coverage Δ
unittests	85.34% <90.00%> (+0.22%)	⬆️

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