Use simple email defaults in base, tls in prod

[elfjes]

Scope and purpose

Argus uses SMTPS 587 for email by default (in settings/base.py). This is a non-obvious default which may confuse third party developers/users (it confused me). This PR sets the default to the more obvious default SMTP 25 (which are also the django settings) and instead sets the Sikt Argus specific defaults (SMTPS 587) in settings/prod.py

Contributor Checklist

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• Added a changelog fragment for towncrier
• Added/amended tests for new/changed code
• Added/changed documentation
• Linted/formatted the code with ruff and djLint, easiest by using pre-commit
• The first line of the commit message continues the sentence "If applied, this commit will ...", starts with a capital letter, does not end with punctuation and is 50 characters or less long. See our how-to
• If applicable: Created new issues if this PR does not fix the issue completely/there is further work to be done
• If this results in changes in the UI: Added screenshots of the before and after
• If this results in changes to the database model: Updated the ER diagram

[sonarqubecloud]

Quality Gate passed

Issues
0 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-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.53%. Comparing base (3242651) to head (bb25342).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1395   +/-   ##
=======================================
  Coverage   78.53%   78.53%           
=======================================
  Files         142      142           
  Lines        5862     5862           
=======================================
  Hits         4604     4604           
  Misses       1258     1258           

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