[BUG] Test connection is broken for data source

[BionIT]

Describe the bug
Enable data source and go to data source management, then go to create data source page, and enter the endpoint and credentials, then click test connection, will see error

To Reproduce
Steps to reproduce the behavior:

1. Enable data source plugin
2. Go to 'data source' management page
3. Click on 'create data source'
4. Enter the endpoint for the data source and credentials
5. Click on 'test connection' and see error

Expected behavior
This is due to customApiRegistry is not added causing it to be undefined.

OpenSearch Version
N/A

Dashboards Version
3.0.0

Plugins

data source plugin

Screenshots

Additional context

Add any other context about the problem here.

[BionIT]

Happy to work on it

[xinruiba]

Duplicate to #5924

[bandinib-amzn]

Happy to work on it

@BionIT Already created the issue #5924 and working on it. Will raise PR in some time.