Return a UserList from /api/v1/admin/users

[zeripath]

The new /api/v1/admin/users endpoint doesn't return a UserList as described on swagger and doesn't return api.User but rather an unsanitised form of models.User.

This PR fixes this.

[lunny]

How about make a function convertUser to convert a models.User to api.User so that two places could use it?

[lunny]

And any test for this API is better!

[codecov-io]

Codecov Report

Merging #6629 into master will increase coverage by 0.05%.
The diff coverage is 89.47%.

@@            Coverage Diff             @@
##           master    #6629      +/-   ##
==========================================
+ Coverage   40.47%   40.52%   +0.05%     
==========================================
  Files         406      406              
  Lines       54484    54492       +8     
==========================================
+ Hits        22052    22084      +32     
+ Misses      29395    29372      -23     
+ Partials     3037     3036       -1

Impacted Files	Coverage Δ
routers/api/v1/user/user.go	25.19% <0%> (+1.49%)	⬆️
routers/api/v1/convert/convert.go	80.68% <100%> (+1.41%)	⬆️
routers/api/v1/admin/user.go	29.24% <83.33%> (+7.26%)	⬆️
modules/log/event.go	64.46% <0%> (-1.53%)	⬇️
routers/repo/view.go	41.08% <0%> (-1%)	⬇️
models/user.go	50.32% <0%> (+0.55%)	⬆️

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[lunny]

But CI build failed.

[zeripath]

Sigh sorry about that.

[techknowlogick]

@zeripath merged 😃 please backport.