Fix the problem of not being able to setup in OS without UTF-8 as default encoding (#7379)

#### What type of PR is this?

/kind bug

#### What this PR does / why we need it:

This PR manually set UTF-8 charset while loading YAML file to fix the problem "java.nio.charset.MalformedInputException: Input length = 1".

#### Which issue(s) this PR fixes:

Fixes https://github.com/halo-dev/halo/issues/6937
Fixes https://github.com/orgs/halo-dev/discussions/7375

#### Does this PR introduce a user-facing change?

```release-note
修复 Windows 下可能无法正常初始化的问题
```

application/src/main/java/run/halo/app/security/preauth/SystemSetupEndpoint.java

@@ -289,7 +289,8 @@ public class SystemSetupEndpoint {
                     var processedContent =
                         PROPERTY_PLACEHOLDER_HELPER.replacePlaceholders(rawContent, properties);
                     // load yaml to unstructured
-                    var stringResource = new InMemoryResource(processedContent);
+                    var stringResource = 
+                        new InMemoryResource(processedContent.getBytes(StandardCharsets.UTF_8));
                     var loader = new YamlUnstructuredLoader(stringResource);
                     return loader.load();
                 })