do not allow user to create private app namespace with the same name as some public app namespace

[nobodyiam]

fixes #1893

[codecov-io]

Codecov Report

Merging #1894 into master will increase coverage by 6.48%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #1894      +/-   ##
============================================
+ Coverage      49.9%   56.38%   +6.48%     
+ Complexity     1916     1068     -848     
============================================
  Files           394      191     -203     
  Lines         12057     5799    -6258     
  Branches       1224      606     -618     
============================================
- Hits           6017     3270    -2747     
+ Misses         5590     2274    -3316     
+ Partials        450      255     -195

Impacted Files	Coverage Δ	Complexity Δ
...ework/apollo/portal/controller/ItemController.java
...o/configservice/wrapper/DeferredResultWrapper.java
...omponent/emailbuilder/GrayPublishEmailBuilder.java
...k/apollo/portal/controller/FavoriteController.java
...apollo/portal/entity/vo/AppRolesAssignedUsers.java
...ponent/emailbuilder/NormalPublishEmailBuilder.java
.../framework/apollo/portal/entity/vo/SystemInfo.java
...rk/apollo/portal/service/NamespaceLockService.java
...k/apollo/portal/spi/ctrip/CtripUserInfoHolder.java
...llo/portal/listener/AppNamespaceDeletionEvent.java
... and 192 more

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