Remove wkw datasource suggestions

[frcroth]

URL of deployed dev instance (used for testing):

• https://___.webknossos.xyz

Instead of unifying wkw exploring with the other explorers, this removes the code related to exploration. The suggestion route is removed. The frontend should still be able to query the data source via readInboxDataSource. @frontend

Steps to test:

TODOs:

• [x] Backend
  • [x] Remove exploring route
  • [x] remove unused code
  • [x] Adapt readInboxDatasource route to support reporting the most current version from disk
• [ ] Frontend
  • [ ] Use readInboxDataSource in dataset settings view (note that it may contain existingDataSourceProperties in case of Unusable json)
  • [ ] Decide what to show exactly in case of invalid json (both invalid fields and json parse error)
  • [ ] In dashboard, always call the link “Settings”, no longer “Import”

Issues:

• fixes #7474

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(Please delete unneeded items, merge only when none are left open)

• [ ] Updated changelog
• [ ] Updated migration guide if applicable
• [ ] Updated documentation if applicable
• [ ] Adapted wk-libs python client if relevant API parts change
• [ ] Removed dev-only changes like prints and application.conf edits
• [ ] Considered common edge cases
• [ ] Needs datastore update after deployment