Drop `ListGroupItem` and `ListGroupItem` `reactstrap` imports

Created by: valerybugakov

Problem statement

We want to get rid of Bootstrap styles. Since reactstrap depends on bootstrap styles, we need to extract component implementations that we use.

Success criteria

1. ListGroup and ListGroupItem imports are removed from the codebase.
2. Instead of these components a combination of HTML and CSS module classes is used.

Implementation details

Rely on the internal implementation of ListGroup and ListGroupItem available here. The component that needs to be updated: SiteAdminSidebar.tsx.

Time estimate

• Pull requests with ~450 lines changed should take 4 hours at maximum. Ping the reviewer in the spec pull request if time-consuming changes are required.
• Split the work into multiple pull requests if the total diff is bigger than 450 lines of code.