Allow PORT to be specified when using bin/dev

[forkata]

Summary

This PR adds a small quality of life improvement when running the development
server through the bin/dev binstub.

Previously running bin/dev would force the development server to run on port
3000, but it is useful to be able to override that if you are running multiple
projects and want to also run the Solidus sandbox app.

Checklist

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.45%. Comparing base (104f813) to head (d0e62d9).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5949      +/-   ##
==========================================
- Coverage   89.54%   89.45%   -0.09%     
==========================================
  Files         782      782              
  Lines       17997    17997              
==========================================
- Hits        16116    16100      -16     
- Misses       1881     1897      +16     

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[tvdeyen]

sank ju