feat: Add required fields for merge of invoices & order models

[mrsaicharan1]

Fixes #6195

Short description of what this resolves:

• Added fields for the event invoices in orders

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.

[mrsaicharan1]

Kept the Event Invoice model as it is to prevent any import breaks. Will refactor it as soon as the payments for event invoices are functional.

[mrsaicharan1]

@iamareebjamal @uds5501 @shreyanshdwivedi Will continue with the additional refactors as soon as this gets reviewed & merged.

[codecov]

Codecov Report

Merging #6196 into development will increase coverage by 0.03%.
The diff coverage is 100%.

@@               Coverage Diff               @@
##           development    #6196      +/-   ##
===============================================
+ Coverage        65.97%   66.01%   +0.03%     
===============================================
  Files              288      288              
  Lines            14526    14532       +6     
===============================================
+ Hits              9584     9593       +9     
+ Misses            4942     4939       -3

Impacted Files	Coverage Δ
app/api/schema/orders.py	89.23% <100%> (+0.34%)	⬆️
app/models/order.py	90.29% <100%> (+0.39%)	⬆️
app/api/helpers/scheduled_jobs.py	24% <0%> (+2.39%)	⬆️

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[kushthedude]

Looks goos

[prateekj117]

LGTM

[iamareebjamal]

Please follow semantic PR conventions so that bot can assign a label and hence PR goes to appropriate category in Release Drafter