dev/sg: introduce linter against OpenTracing usages

Created by: bobheadxi

Based on https://github.com/sourcegraph/sourcegraph/pull/40949#issuecomment-1232949300 there are major issues with context propagation in OpenTracing even with the OpenTracing to OpenTelemetry bridge set up. To expedite migration and prevent further usage, we add a simple linter that just targets imports for now - this can later be expanded to ban new API usages as well.

Test plan

CI passes