Add development environment a default mailer port configuration

[juankuquintana]

At the moment, when opening a mailer link in development mode it does not include the port so it has to be manually added. This PR addresses such problem by adding a default port in the configuration.

• A constant created within the Gemcutter module is possible, but decided to minimize changes.
• Only changed development and test environment to minimize modifications.
• Used a default port on test environment to test the URL link does contain the port but can be removed and will work, there just won't be a test for it.
• This PR does not address starting the app with a custom port like rails s -p 3001 as considering such scenario requires code that could be considered "hacky".

Testing

1. Go to http://localhost:3001/rails/mailers/
2. Open a mailer that contains a link to the application
3. Verify that the link contains the current application port

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Closes #3728

[codecov]

Codecov Report

Merging #3792 (6a95186) into master (0240dc2) will decrease coverage by 0.01%.
The diff coverage is n/a.

❗ Current head 6a95186 differs from pull request most recent head 45c2494. Consider uploading reports for the commit 45c2494 to get more accurate results

@@            Coverage Diff             @@
##           master    #3792      +/-   ##
==========================================
- Coverage   98.81%   98.81%   -0.01%     
==========================================
  Files         214      213       -1     
  Lines        5250     5239      -11     
==========================================
- Hits         5188     5177      -11     
  Misses         62       62              

see 5 files with indirect coverage changes

[juankuquintana]

I've fixed the Rubocop failing scenarios 👍

[jenshenny]

Out of curiosity, does 31337 signify anything?

[juankuquintana]

Out of curiosity, does 31337 signify anything?

No, it's a random port number I configured in the test environment 😅 .

[jenshenny]

Thanks @juankuquintana!