Add number of installs to the extension card and details page

Created by: AlicjaSuska

##Description

This issue adds the number of installs of the extension card and details page in order to provide social proof.

##Design specification

• Card, Icon - mdi:account-group
• Solving low user count problem (Figma), let's introduce 4 breakpoints for the count: <20, 20+, 50+, 100+ (Slack thread for context).
• Details column (new section)
• green arrow and 'X most installed extension' text should appear next to the 10 most installed extensions
• on hover on the info icon (details page) and the installs number (card), we should show the tooltip that explains how we calculate it: Number of extension installations across all Sourcegraph instances @Joelkw could you please review the text. Thank you!