Allow plugin to listen the event the plugin has started

[JohnNiang]

What type of PR is this?

/kind feature
/area core
/milestone 2.17.x

What this PR does / why we need it:

This PR add support for allowing plugin to listen the event that the plugin has started. Below is an example of listening the event in plugin:

    @EventListener
    void onPluginStartedEvent(PluginStartedEvent event) {
        // do something.
    }

See #5339 (comment) for more.

Which issue(s) this PR fixes:

Fixes #5339 (comment)

Special notes for your reviewer:

1. Create a plugin, add the listener above and write some logs
2. Build and install the plugin
3. Start plugin and see the logs you wrote

Does this PR introduce a user-facing change?

支持在插件中监听已启动事件

[codecov]

Codecov Report

Attention: Patch coverage is 7.69231% with 12 lines in your changes missing coverage. Please review.

Project coverage is 57.19%. Comparing base (bc10336) to head (70f5e17).
Report is 44 commits behind head on main.

Files	Patch %	Lines
...in/java/run/halo/app/plugin/HaloPluginManager.java	9.09%	10 Missing ⚠️
.../run/halo/app/plugin/event/PluginStartedEvent.java	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #6234      +/-   ##
============================================
+ Coverage     54.51%   57.19%   +2.68%     
- Complexity     3523     3719     +196     
============================================
  Files           646      647       +1     
  Lines         21862    21974     +112     
  Branches       1528     1538      +10     
============================================
+ Hits          11917    12567     +650     
+ Misses         9328     8798     -530     
+ Partials        617      609       -8     

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[guqing]

/lgtm

[f2c-ci-robot]

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