[BUG][Discover-Next] Invalid security token error when using query assist with MDS

[abbyhu2000]

Describe the bug
When testing MDS with discover:

It is able to get the suggested questions using query assist. However, after pressing generate button, the query failed to generate due to

{"error":{"reason":"System Error","details":"Error from remote service: 
{\"message\":\"The security token included in the request is invalid.\"}",
"type":"OpenSearchStatusException"},"status":403}`

To Reproduce
Steps to reproduce the behavior:

1. Installed MDS DashboardsPlugin and queryEnhancements in /plugins folder and bootstrap in NeoDashboardsPlugin
2. Modify corresponding config yml files values and start up a MDS dashboard
3. Created data source connection and index pattern
4. Turned on query enhancement toggle
5. Go to discover

Screenshots

[joshuali925]

1. is NeoDashboardsPlugin relevant?
2. The security token included in the request is invalid error message is kind of clear, how was the model setup and is the security token valid?