docs: add downloadPluginPresets step for build documentation (#243)

完善开发环境构建的文章，添加下载预设插件的步骤。

Fixes #242 
Ref https://github.com/halo-dev/halo/issues/4418#issuecomment-1677354115

/kind documentation

```release-note
None
```

docs/developer-guide/core/build.md

@@ -69,6 +69,18 @@ pnpm build
 cd path/to/halo
 ```
 
+下载预设插件：
+
+```bash
+# Windows
+./gradlew.bat downloadPluginPresets
+
+# macOS / Linux
+./gradlew downloadPluginPresets
+```
+
+构建：
+
 ```bash
 # Windows
 ./gradlew.bat clean build -x check

versioned_docs/version-2.7/developer-guide/core/build.md

@@ -69,6 +69,18 @@ pnpm build
 cd path/to/halo
 ```
 
+下载预设插件：
+
+```bash
+# Windows
+./gradlew.bat downloadPluginPresets
+
+# macOS / Linux
+./gradlew downloadPluginPresets
+```
+
+构建：
+
 ```bash
 # Windows
 ./gradlew.bat clean build -x check

versioned_docs/version-2.8/developer-guide/core/build.md

@@ -69,6 +69,18 @@ pnpm build
 cd path/to/halo
 ```
 
+下载预设插件：
+
+```bash
+# Windows
+./gradlew.bat downloadPluginPresets
+
+# macOS / Linux
+./gradlew downloadPluginPresets
+```
+
+构建：
+
 ```bash
 # Windows
 ./gradlew.bat clean build -x check