refactor(general): better encapsulate user profile implementation

[julio-lopez]

Motivation: better encapsulate the implementation details for user profiles, in particular with respect to password hashing schemes.

• Pass hash version to computePasswordHash to encapsulate the internal representation of hashing schemes in user profiles.
• Add user.GetNewProfile helper to initialize a user.Profile in the user package. This avoids exposing hashing versions outside of the user package.

[codecov]

Codecov Report

Attention: Patch coverage is 85.18519% with 4 lines in your changes missing coverage. Please review.

Project coverage is 77.20%. Comparing base (cb455c6) to head (2061edf).
Report is 160 commits behind head on master.

Files	Patch %	Lines
internal/user/user_manager.go	75.00%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3910      +/-   ##
==========================================
+ Coverage   75.86%   77.20%   +1.33%     
==========================================
  Files         470      482      +12     
  Lines       37301    28803    -8498     
==========================================
- Hits        28299    22237    -6062     
+ Misses       7071     4660    -2411     
+ Partials     1931     1906      -25     

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