Run staging as RAILS_ENV=production

[martinemde]

Avoid accidental differences between staging and production. Describe all differences in ENV.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.07%. Comparing base (a786900) to head (ee0a313).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5308      +/-   ##
==========================================
- Coverage   97.14%   97.07%   -0.08%     
==========================================
  Files         457      457              
  Lines        9564     9564              
==========================================
- Hits         9291     9284       -7     
- Misses        273      280       +7     

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[simi]

We should run staging as separate env with RAILS_ENV=staging, but copy production config (as done in staging.rb) and don't rely on Rails.env.production?, but on feature config.

[martinemde]

Closing in favor of the less scary #5309, for now.