feat: update event invoice payment follow ups

[uds5501]

Fixes fossasia/open-event-frontend#3130

Short description of what this resolves:

Sends modified follow up emails for event invoice payments

Checklist

• I have read the Contribution & Best practices Guide and my PR follows them.
• My branch is up-to-date with the Upstream development branch.
• The unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

• All the functions created/modified in this PR contain relevant docstrings.

[codecov]

Codecov Report

Merging #6391 into development will not change coverage.
The diff coverage is 33.33%.

@@             Coverage Diff              @@
##           development    #6391   +/-   ##
============================================
  Coverage        65.16%   65.16%           
============================================
  Files              287      287           
  Lines            14810    14810           
============================================
  Hits              9651     9651           
  Misses            5159     5159

Impacted Files	Coverage Δ
app/api/helpers/scheduled_jobs.py	20.93% <0%> (ø)	⬆️
app/__init__.py	87.63% <100%> (ø)	⬆️

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