Make IsSubdomainOf variadic

[pajlada]

Pull request checklist:

• CHANGELOG.md was updated, if applicable

Description

• Make IsSubdomainOf variadic
• Add variadic tests

[pajlada]

[codecov]

Codecov Report

Merging #526 (610c513) into master (438b0c7) will increase coverage by 0.05%.
Report is 1 commits behind head on master.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #526      +/-   ##
==========================================
+ Coverage   47.13%   47.19%   +0.05%     
==========================================
  Files          99       99              
  Lines        3717     3721       +4     
==========================================
+ Hits         1752     1756       +4     
  Misses       1914     1914              
  Partials       51       51              

Files Changed	Coverage Δ
pkg/utils/url.go	18.46% <100.00%> (+5.34%)	⬆️

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more