web: integrate `@sourcegraph/stylelint-plugin-sourcegraph` and ban `bootstrap` imports
Created by: valerybugakov
Context
We work on dropping bootstrap and reactstrap dependencies in favor of the Wildcard component library.
This PR adds a linter rule that bans new bootstrap imports. Existing imports will be migrated as a part of https://github.com/sourcegraph/sourcegraph/issues/29200. For now, linter errors are disabled for existing bootstrap imports.
Test plan
yarn lint:css:all should pass locally
App preview:
Check out the client app preview documentation to learn more.