fix: not clearing the template engine cache after upgrading the theme

[minliacom]

What type of PR is this?

/kind improvement

What this PR does / why we need it:

通过在模板引擎管理器里添加clearCache方法，在升级主题后进行缓存刷新，让新模板内容生效。

Which issue(s) this PR fixes:

Fixes #2953

Special notes for your reviewer:

Does this PR introduce a user-facing change?

NONE

[CLAassistant]

All committers have signed the CLA.

[ruibaby]

感谢 @minliacom 的贡献，在 Review 前请先签署我们的 CLA 协议：#2970 (comment)

另外，测试似乎没有通过。

[guqing]

我忽略了一点 卸载的时候应该要在 reconciler 清除缓存，需要在 ThemeResolver 中添加一个根据 theme name 得到 ThemeContext 的方法

[minliacom]

我忽略了一点 卸载的时候应该要在 reconciler 清除缓存，需要在 ThemeResolver 中添加一个根据 theme name 得到 ThemeContext 的方法

嗯，我按这样尝试一下

[JohnNiang]

如果要更细致的话，在切换主题的时候也得清理 Thymeleaf 缓存。

[JohnNiang]

Hi @minliacom ，建议当前 PR 只解决升级时清理缓存即可。暂时不用管删除和切换主题的情况。

[minliacom]

Hi @minliacom ，建议当前 PR 只解决升级时清理缓存即可。暂时不用管删除和切换主题的情况。

那我先把删除和切换的代码删除了再提交

[guqing]

/approve
经测试符合预期 🎉

[ruibaby]

/lgtm

[JohnNiang]

/hold

Please wait for my code review.

[JohnNiang]

/unhold

[ruibaby]

#2970 (comment)

这里有一个名为 Your Name 的用户名没有签署 CLA，导致无法合并。建议进行以下操作：

git fetch upstream/main

git reset --soft upstream/main

git add .

git commit -m "fix: not clearing the template engine cache after upgrading the theme"

git push -f

[minliacom]

@ruibaby OK了

[JohnNiang]

/lgtm

[f2c-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: guqing, JohnNiang

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[ruibaby]

@halo-dev/sig-halo 其他需要清理缓存的情况是否需要提交 issue 呢？