[BUG] notebook visualization not working with OpenSearchDashboards saved objects when data source is enabled

[zengyan-amazon]

What is the bug?
In https://github.com/opensearch-project/dashboards-observability/blame/main/server/routes/notebooks/vizRouter.ts#L15 , when multi data source is enabled, the route handler try to work with visualizations in the OSD metadata index in that particular data source, instead of working with the visualizations in the saved object metadata index with local OpenSearch Dashboards server.

What is the expected behavior?
use savedobjectclient to get visualzations instead of querying metadata index directly

What is your host/environment?

• OS: [e.g. iOS]
• Version [e.g. 22]
• Plugins

Do you have any screenshots?
If applicable, add screenshots to help explain your problem.

Do you have any additional context?
Add any other context about the problem.

[ps48]

@zengyan-amazon This PR already solved the issue to use savedObjectClient: #2241. I see some issue with limited visualization showing up as the reponse is capped to show 20 items. I'll check further on how to increase that to some considerable number as we don't have pagination supported in the notebooks UI.