refactor: logic of theme management modal

[ruibaby]

What type of PR is this?

/area ui
/kind improvement
/milestone 2.16.x

What this PR does / why we need it:

优化主题管理弹窗的显示逻辑，改为在未打开弹窗组件的时候不渲染组件，减少不必要的请求。

before:

after:

Which issue(s) this PR fixes:

Does this PR introduce a user-facing change?

优化主题管理弹窗的显示逻辑，减少不必要的请求。

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 56.76%. Comparing base (5fdf6c0) to head (94cc223).
Report is 192 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #5966      +/-   ##
============================================
- Coverage     56.91%   56.76%   -0.15%     
- Complexity     3319     3486     +167     
============================================
  Files           587      611      +24     
  Lines         18968    20523    +1555     
  Branches       1401     1419      +18     
============================================
+ Hits          10795    11650     +855     
- Misses         7594     8293     +699     
- Partials        579      580       +1     

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[guqing]

/lgtm

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarCloud

[JohnNiang]

/lgtm

[f2c-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: JohnNiang

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• ui/OWNERS [JohnNiang]

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