Support hooking user creation

[JohnNiang]

What type of PR is this?

/kind feature
/area core
/milestone 2.20.x

What this PR does / why we need it:

This PR adds support for hooking user creating. Plugin developers can define extension points of UserPreCreatingHandler and UserPostCreatingHandler to do something else.

Does this PR introduce a user-facing change?

支持在插件中定义用户创建的前置和后置处理器

[sonarcloud]

Quality Gate passed

Issues
2 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 57.23%. Comparing base (eff73dc) to head (cb2107f).
Report is 37 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #6945      +/-   ##
============================================
+ Coverage     56.99%   57.23%   +0.23%     
- Complexity     3999     4005       +6     
============================================
  Files           714      712       -2     
  Lines         24110    24123      +13     
  Branches       1585     1588       +3     
============================================
+ Hits          13742    13806      +64     
+ Misses         9756     9704      -52     
- Partials        612      613       +1     

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[JohnNiang]

I'm going to merge this PR as quick as possible for a quick verification.

[ruibaby]

/lgtm

[f2c-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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