Return more detail diagnostics from `check.Runner.Check()`

Created by: burmudar

From https://github.com/sourcegraph/sourcegraph/pull/37196#issuecomment-1160628731

@burmudar you might want to explore digging into check.Runner.Check() to have it return more detailed diagnostics (report and error perhaps?): https://sourcegraph.com/github.com/sourcegraph/sourcegraph@6ab63777c67ea1c0c6e81b17f5ad8985d27251bc/-/blob/dev/sg/internal/check/runner.go?L48-67 😁

The goal is to deprecate sg doctor in favour of a unified sg setupv2 -check (with setupv2 becoming just setup when https://github.com/sourcegraph/sourcegraph/tree/devx/sg-setup2-ubuntu is done!)