Fix site-admin client e2e tests
Created by: erzhtor
Follow-up on https://github.com/sourcegraph/sourcegraph/pull/40989.
It turned out that there were e2e test selectors which were checking for old "statistics/overview" page sections. However, in a recent PR, it was replaced with a new "analytics/overview" page. This PR adds test-id selectors to the corresponding sections.
Test plan
- Check the diff, if possible run client e2e tests locally.