[Datasources] Address Remaining Items in Datasource Selector

[mengweieric]

Is your feature request related to a problem? Please describe.

Due to time constraints, some review comments have not been addressed. This issue is for tracking those remaining tasks need to be addressed in the PR #5167 .

Describe the solution you'd like

Addressing all reviews after the merge, including:
- add / improve interfaces and types
- code movement of datasource registration from discover to data plugin

• Adjustments for datasource API definitions
  • removing multiple selectable API
  • add type to datasource and remove hardcoding type name mapping
    - using i18n for user facing text
• Unit / E2E test coverage

[anirudha]

lets target this at 2.12 or sooner

[anirudha]

In the next release we should move this to the view-switcher asap

[mengweieric]

Spoke with @ashwin-pc on this issue that we will:

• Remove this issue from 2.12 release
• Add tests to datasource code lines that still need coverages
• Make change to datasource interface addressing item 'Adjustments for datasource API definitions' after 2.12 when we'd settled new datasource interface designs