[Admin Analytics] update code intel stats

Created by: thenamankumar

• Update code intel stats to show in app vs code host events
• Add alert on users stats page to mention that its experimental
• Flip working on feature flag to make admin analytics enabled by default

Users Stats

Code Intel Stats

Test plan

• visit https://sourcegraph.test:3443/site-admin/analytics/code-intel
• visit https://sourcegraph.test:3443/site-admin/analytics/users