[8.15] [Kibana data view] Fix issue empty user-hash in data view requ…

…est headers (elastic#197863)

to fix not compliant HTTP request

## Summary

Fix not compliant HTTP request
for example, request "GET
/s/<space>/internal/data_views/fields?pattern=abc" Sometimes request
headers have a user-hash field with an empty value and this makes the
request not HTTP compliant in some scenarios the request will be dropped
by WAF or by another security edge for example.


![image](https://github.com/user-attachments/assets/de606665-12e6-475c-a2e4-c2e594957f11)

---------

Co-authored-by: kibanamachine <[email protected]>
Co-authored-by: Elastic Machine <[email protected]>
Co-authored-by: mabdelgaber.SEC <[email protected]>

src/plugins/data_views/public/data_views/data_views_api_client.test.ts

@@ -30,9 +30,6 @@ describe('IndexPatternsApiClient', () => {
     expect(fetchSpy).toHaveBeenCalledWith(expectedPath, {
       // not sure what asResponse is but the rest of the results are useful
       asResponse: true,
-      headers: {
-        'user-hash': '',
-      },
       query: {
         allow_hidden: undefined,
         allow_no_index: undefined,

src/plugins/data_views/public/data_views/data_views_api_client.ts

@@ -56,6 +56,7 @@ export class DataViewsApiClient implements IDataViewsApiClient {
     const userId = await this.getCurrentUserId();
 
     const userHash = userId ? await sha1(userId) : '';
+    const headers = userHash ? { 'user-hash': userHash } : undefined;
 
     const request = body
       ? this.http.post<T>(url, { query, body, version, asResponse })
@@ -64,7 +65,7 @@ export class DataViewsApiClient implements IDataViewsApiClient {
           version,
           ...cacheOptions,
           asResponse,
-          headers: { 'user-hash': userHash },
+          headers,
         });
 
     return request.catch((resp) => {