[BUG] MD: datasource id is required if there is no open-search hosts config

[xinruiba]

Describe the bug

When datasource id is empty the search returns 500 error which is unexpected since this is more of input error.

To Reproduce
Steps to reproduce the behavior:

1. Turn On "data_source.enabled" config
2. Run OSD
3. Send following request:
   curl 'localhost:5601/internal/search/opensearch' --data '{"params": {"index":"movies*","body":{},"preference":1697624613679}}' -H 'x-amzn-aosd-app-id:random' -H 'osd-xsrf:osd-fetch' -H 'Content-Type:application/json'
4. See returned error code is 500

Expected behavior
When datasourceid is empty or datasouce context is empty and there is no opernsearch hosts specified, then the request is invalid and should return 400 error code

OpenSearch Version
2.12

Dashboards Version
Please list the version of OpenSearch Dashboards being used.

Plugins

DataSource

Screenshots
N/A

Host/Environment (please complete the following information):

• OS: [e.g. iOS]
• Browser and version [e.g. 22]

Additional context
N/A

[xinruiba]

Happy to work on it

[xinruiba]

fixed in #5882 . Closing this issue.