refactor: trigger plugin config updated event at startup

[guqing]

What type of PR is this?

/kind improvement
/area core
/milestone 2.18.x

What this PR does / why we need it:

插件启动时触发一次插件配置更新事件以便进行资源初始化操作

之前配置插件完后重启/升级插件无法监听到事件则不方便初始化资源需要通过再次监听插件启动事件来实现，现在改为插件启动时可以监听到

Does this PR introduce a user-facing change?

插件启动时触发一次插件配置更新事件以便进行资源初始化操作

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 10 lines in your changes missing coverage. Please review.

Project coverage is 58.29%. Comparing base (bc10336) to head (733f1da).
Report is 91 commits behind head on main.

Files	Patch %	Lines
...halo/app/plugin/DefaultReactiveSettingFetcher.java	0.00%	10 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #6346      +/-   ##
============================================
+ Coverage     54.51%   58.29%   +3.78%     
- Complexity     3523     3764     +241     
============================================
  Files           646      646              
  Lines         21862    21979     +117     
  Branches       1528     1545      +17     
============================================
+ Hits          11917    12813     +896     
+ Misses         9328     8547     -781     
- Partials        617      619       +2     

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[ruibaby]

/lgtm

[JohnNiang]

/lgtm

[f2c-ci-robot]

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