[27.0 backport] re-introduced support for port numbers in docker registry URL

[thaJeztah]

• backport re-introduced support for port numbers in docker registry URL #5195

- What I did

• this is a fix for a regression introduced by use local ConvertToHostname() implementation #3599
• re-introduced support for port numbers in docker registry URL
• fixes v26.1.4 -> 27.0.1: "docker login https://myregistry:444/" loses port #5194

- How to verify it

• added new test cases and ran docker buildx bake test

- Description for the changelog

Fix a regression that caused port numbers to be ignored when parsing a Docker registry URL.

- A picture of a cute animal (not mandatory but encouraged)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 61.43%. Comparing base (fce24d5) to head (217971d).

Additional details and impacted files

@@           Coverage Diff           @@
##             27.0    #5197   +/-   ##
=======================================
  Coverage   61.42%   61.43%           
=======================================
  Files         298      298           
  Lines       20797    20799    +2     
=======================================
+ Hits        12775    12777    +2     
  Misses       7109     7109           
  Partials      913      913