[BUG] Multiple datasource UI fixes

[Flyingliuhub]

Describe the bug

The current 'dev tools' is using text "Select a Data Source" which should be "Select a data source", and when user is using the feature flag to disable other authentication, the other authentication type should be disabled in the drop down list.

To Reproduce
Steps to reproduce the behavior:

1. Go to 'Dev Tools'
2. Navigate to right top corner, it is showing up "Select a Data Source"

Expected behavior
It should be "Select a data source"

OpenSearch Version
2.11

Dashboards Version
2.11

Plugins

N/A

Screenshots

Host/Environment (please complete the following information):

• OS: MacOS
• Browser and version: firefox 115.5.0esr

Additional context

N/A

[bandinib-amzn]

It got fixed in #5475