Allow empty op number

[sainak]

This pull request updates the code to allow for an empty op number. It also includes several other changes and fixes related to patient numbers and validation.

TODO:

• rollback migration on dev instance

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 62.16%. Comparing base (7c85464) to head (facc733).

Files	Patch %	Lines
...e/facility/api/serializers/patient_consultation.py	50.00%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1954      +/-   ##
==========================================
+ Coverage   62.14%   62.16%   +0.02%     
==========================================
  Files         221      221              
  Lines       12198    12203       +5     
  Branches     1740     1742       +2     
==========================================
+ Hits         7580     7586       +6     
+ Misses       4310     4308       -2     
- Partials      308      309       +1     

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