fix: the exception of plugin context has been closed when plugin restart

[guqing]

What type of PR is this?

/kind bug
/area core
/milestone 2.0

What this PR does / why we need it:

BasePlugin 持有了一个当前插件的 PluginApplicationContext 当插件停止后重新启用会获取到旧的 PluginApplicationContext，之前之所以这样写的目的只是插件的这个 BasePlugin 不支持依赖注入，目前已经支持所以不在这样解决问题

日志：

Caused by: java.lang.IllegalStateException: run.halo.app.plugin.PluginApplicationContext@6baf2671 has been closed already
	at org.springframework.context.support.AbstractApplicationContext.assertBeanFactoryActive(AbstractApplicationContext.java:1125) ~[spring-context-6.0.0-M5.jar:6.0.0-M5]
	at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1158) ~[spring-context-6.0.0-M5.jar:6.0.0-M5]
	at run.halo.app.plugin.SpringExtensionFactory.create(SpringExtensionFactory.java:102) ~[classes/:2.0.0-alpha.1]
	at org.pf4j.ExtensionWrapper.getExtension(ExtensionWrapper.java:37) ~[pf4j-3.7.0.jar:3.7.0]
	at org.pf4j.AbstractPluginManager.getExtensions(AbstractPluginManager.java:971) ~[pf4j-3.7.0.jar:3.7.0]
	at run.halo.app.plugin.HaloPluginManager.getExtensions(HaloPluginManager.java:118) ~[classes/:2.0.0-alpha.1]
	at run.halo.app.plugin.ExtensionComponentsFinder.getExtensions(ExtensionComponentsFinder.java:36) ~[classes/:2.0.0-alpha.1]
	at run.halo.app.theme.dialect.CommentElementTagProcessor.doProcess(CommentElementTagProcessor.java:49) ~[classes/:2.0.0-alpha.1]
	at org.thymeleaf.processor.element.AbstractElementTagProcessor.process(AbstractElementTagProcessor.java:95) ~[thymeleaf-3.1.0.M2.jar:3.1.0.M2]
	at org.thymeleaf.util.ProcessorConfigurationUtils$ElementTagProcessorWrapper.process(ProcessorConfigurationUtils.java:633) ~[thymeleaf-3.1.0.M2.jar:3.1.0.M2]
	at org.thymeleaf.engine.ProcessorTemplateHandler.handleStandaloneElement(ProcessorTemplateHandler.java:918) ~[thymeleaf-3.1.0.M2.jar:3.1.0.M2]
	at org.thymeleaf.engine.StandaloneElementTag.beHandled(StandaloneElementTag.java:228) ~[thymeleaf-3.1.0.M2.jar:3.1.0.M2]
	at org.thymeleaf.engine.Model.process(Model.java:282) ~[thymeleaf-3.1.0.M2.jar:3.1.0.M2]
	at org.thymeleaf.engine.ProcessorTemplateHandler.handleStandaloneElement(ProcessorTemplateHandler.java:1204) ~[thymeleaf-3.1.0.M2.jar:3.1.0.M2]
	at org.thymeleaf.engine.StandaloneElementTag.beHandled(StandaloneElementTag.java:228) ~[thymeleaf-3.1.0.M2.jar:3.1.0.M2]
	at org.thymeleaf.engine.Model.process(Model.java:282) ~[thymeleaf-3.1.0.M2.jar:3.1.0.M2]
	at org.thymeleaf.engine.ProcessorTemplateHandler.handleOpenElement(ProcessorTemplateHandler.java:1587) ~[thymeleaf-3.1.0.M2.jar:3.1.0.M2]
	at org.thymeleaf.engine.OpenElementTag.beHandled(OpenElementTag.java:205) ~[thymeleaf-3.1.0.M2.jar:3.1.0.M2]
	at org.thymeleaf.engine.TemplateModel.process(TemplateModel.java:136) ~[thymeleaf-3.1.0.M2.jar:3.1.0.M2]
	at org.thymeleaf.engine.TemplateManager.parseAndProcess(TemplateManager.java:592) ~[thymeleaf-3.1.0.M2.jar:3.1.0.M2]
	at org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1103) ~[thymeleaf-3.1.0.M2.jar:3.1.0.M2]
	at org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1077) ~[thymeleaf-3.1.0.M2.jar:3.1.0.M2]
	at run.halo.app.theme.engine.SpringWebFluxTemplateEngine.lambda$createFullStream$0(SpringWebFluxTemplateEngine.java:202) ~[classes/:2.0.0-alpha.1]
	at reactor.core.publisher.MonoCreate.subscribe(MonoCreate.java:58) ~[reactor-core-3.5.0-M4.jar:3.5.0-M4]
	at reactor.core.publisher.Mono.subscribe(Mono.java:4321) ~[reactor-core-3.5.0-M4.jar:3.5.0-M4]
	at reactor.core.publisher.MonoSubscribeOn$SubscribeOnSubscriber.run(MonoSubscribeOn.java:126) ~[reactor-core-3.5.0-M4.jar:3.5.0-M4]
	at reactor.core.scheduler.WorkerTask.call(WorkerTask.java:84) ~[reactor-core-3.5.0-M4.jar:3.5.0-M4]
	at reactor.core.scheduler.WorkerTask.call(WorkerTask.java:37) ~[reactor-core-3.5.0-M4.jar:3.5.0-M4]
	at java.base/java.util.concurrent.FutureTask.run(Unknown Source) ~[na:na]
	at java.base/java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(Unknown Source) ~[na:na]
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) ~[na:na]
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) ~[na:na]
	at java.base/java.lang.Thread.run(Unknown Source) ~[na:na]

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

how to test:

1. 安装一个插件
2. 启用它再停止它，如此反复，没有抛出异常即可

/cc @halo-dev/sig-halo

Does this PR introduce a user-facing change?

修复插件重启引起的异常

[JohnNiang]

/approve

[f2c-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: JohnNiang

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[ruibaby]

/lgtm

实际测试在启用停止插件没有出现异常。