chore(ref): Refactor order complete logic

[iamareebjamal]

Fixes #7412

Organizer will now receive emails about ticket purchase

[codecov]

Codecov Report

Merging #7418 into development will increase coverage by 0.53%.
The diff coverage is 50.00%.

@@               Coverage Diff               @@
##           development    #7418      +/-   ##
===============================================
+ Coverage        64.74%   65.28%   +0.53%     
===============================================
  Files              265      265              
  Lines            13319    13205     -114     
===============================================
- Hits              8624     8621       -3     
+ Misses            4695     4584     -111     

Impacted Files	Coverage Δ
app/api/custom/attendees.py	48.00% <0.00%> (ø)
app/api/custom/invoices.py	36.95% <0.00%> (+0.78%)	⬆️
app/api/helpers/system_mails.py	100.00% <ø> (ø)
app/api/helpers/mail.py	40.76% <30.00%> (-0.51%)	⬇️
app/api/helpers/ticketing.py	52.73% <33.33%> (+3.34%)	⬆️
app/api/helpers/order.py	63.04% <35.71%> (-3.90%)	⬇️
app/api/custom/orders.py	70.73% <50.00%> (+33.01%)	⬆️
app/api/orders.py	43.39% <66.66%> (+2.02%)	⬆️
app/api/helpers/notification.py	78.31% <75.00%> (ø)
app/models/order.py	88.50% <75.00%> (-1.91%)	⬇️
... and 2 more

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[mariobehling]

Nice!