implement getDashboards
Created by: unclejustin
Note: This PR is based on and should merge into this integration PR #26382
This is a minimal implementation for the getDashboards
API method.
I have made the properties from settings cascade that do not appear in the graphql API optional. This allows us to leverage Typescript by alerting us directly to the places where we need to support the new API.
For this PR I am simply throwing errors where support is missing to try and reduce complexity. Addressing these errors will be handled in a future PR.
Closes https://github.com/sourcegraph/sourcegraph/issues/25878