fix: Fixed migration error and downgrade function

[mrsaicharan1]

Fixes #6128

Short description of what this resolves:

Changes proposed in this pull request:

• Previously, order_expiry_time was allowed to be NULL, fixed downgrade method
• server_default needs to be a string

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.

[shreyanshdwivedi]

Checked locally. Working fine now. Thank you

[mrsaicharan1]

@uds5501 @iamareebjamal Please review.

[uds5501]

Looks good!

[codecov]

Codecov Report

Merging #6129 into development will increase coverage by 0.02%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           development    #6129      +/-   ##
===============================================
+ Coverage         66.5%   66.52%   +0.02%     
===============================================
  Files              286      286              
  Lines            14275    14275              
===============================================
+ Hits              9494     9497       +3     
+ Misses            4781     4778       -3

Impacted Files	Coverage Δ
app/api/helpers/scheduled_jobs.py	26.31% <0%> (+3.15%)	⬆️

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