[CLIENT-3510] Add support for adding a PKI user without a password

[juliannguyen4]

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 91.93548% with 5 lines in your changes missing coverage. Please review.

Project coverage is 82.00%. Comparing base (7256716) to head (875f84b). Report is 3 commits behind head on dev.

Files with missing lines	Patch %	Lines
src/main/client/admin.c	93.75%	3 Missing :warning:
src/main/conversions.c	85.71%	2 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #787      +/-   ##
==========================================
+ Coverage   81.92%   82.00%   +0.08%     
==========================================
  Files          99       99              
  Lines       14671    14698      +27     
==========================================
+ Hits        12019    12053      +34     
+ Misses       2652     2645       -7     

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