displayName (and other config fields) not included in uploadToFileSearchStore request

#### Environment details

- Programming language: Java
- OS: macOS
- Language runtime version: Java 11+
- Package version: 1.38.0

#### Steps to reproduce

1. Create an `UploadToFileSearchStoreConfig` with `displayName` set:

```java
UploadToFileSearchStoreConfig config = UploadToFileSearchStoreConfig.builder()
.displayName("my-document")
.build();

client.fileSearchStores.uploadToFileSearchStore(storeName, file, config);
```

2. The displayName is silently dropped from the actual API request.

Root Cause

In `FileSearchStores.java`, the `getUploadUrl()` method (line 910-915) creates a new `UploadToFileSearchStoreConfig` with only `httpOptions` and `shouldReturnHttpResponse`, discarding the original `config`'s fields:

```
UploadToFileSearchStoreResumableResponse response =
privateUploadToFileSearchStore(
fileSearchStoreName,
UploadToFileSearchStoreConfig.builder()
.httpOptions(httpOptions)
.shouldReturnHttpResponse(true)
.build());
```

This also affects customMetadata and chunkingConfig.

Expected Behavior

The original config fields (displayName, customMetadata, chunkingConfig) should be preserved and included in the request to the API.