Cleanup: Adds custom migration to clean prescriptions

[rithviknishad]

Proposed Changes

• Added a custom migration that will update all prescriptions that are is_migrated=True and frequency__isnull=False to have uppercase frequency.

Associated Issue

• Fixes Prescriptions Migration Cleanup: Correct migrated frequency choice from lowercase to UPPERCASE choices #1353
  The custom migration will update all migrated prescriptions whose frequencies are not null to uppercase frequency.

Architecture changes

• Remove this section if not used

Merge Checklist

• Tests added/fixed
• Update docs in /docs
• Linting Complete
• Any other necessary step

Only PR's with test cases included and passing lint and test pipelines will be reviewed

@coronasafe/code-reviewers

[codecov-commenter]

Codecov Report

Patch and project coverage have no change.

Comparison is base (e5e7453) 56.66% compared to head (4921cec) 56.66%.

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Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1361   +/-   ##
=======================================
  Coverage   56.66%   56.66%           
=======================================
  Files         195      195           
  Lines        9862     9862           
  Branches     1655     1655           
=======================================
  Hits         5588     5588           
  Misses       4220     4220           
  Partials       54       54           

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