dev/sg: add go directive linter
Created by: bobheadxi
Closes https://github.com/sourcegraph/sourcegraph/pull/35085 as an alternative implementation, part of https://github.com/sourcegraph/sourcegraph/issues/33363
Test plan
Add a failing check:
Created by: bobheadxi
Closes https://github.com/sourcegraph/sourcegraph/pull/35085 as an alternative implementation, part of https://github.com/sourcegraph/sourcegraph/issues/33363
Add a failing check: