Add created_at date to list display in admin

[amakarudze]

• Add created_at date to the list display for event applications.
• Add created_at date to the list display for events.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.23%. Comparing base (2457351) to head (9bc200b).
Report is 22 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1071   +/-   ##
=======================================
  Coverage   81.23%   81.23%           
=======================================
  Files         101      101           
  Lines        2985     2985           
  Branches      273      273           
=======================================
  Hits         2425     2425           
  Misses        506      506           
  Partials       54       54           

Files with missing lines	Coverage Δ
core/admin/event.py	80.73% <ø> (ø)
organize/admin.py	60.00% <ø> (ø)

... and 1 file with indirect coverage changes

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[marksweb]

LGTM 👍