add soft delete support to "delete user"

[JKFSOM]

What kind of change does this PR introduce?

Feature.

What is the current behavior?

No support for soft deletion.

What is the new behavior?

Optionally request soft deletion.

Additional context

Issue: #375

[codecov]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (fbddd6d) 45.37% compared to head (5471167) 45.40%.
Report is 1 commits behind head on main.

Files	Patch %	Lines
gotrue/_sync/api.py	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #376      +/-   ##
==========================================
+ Coverage   45.37%   45.40%   +0.03%     
==========================================
  Files          23       23              
  Lines        1955     1958       +3     
==========================================
+ Hits          887      889       +2     
- Misses       1068     1069       +1     

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[silentworks]

Thank you for this PR.