AI Impact: Add Code Suggestion Unique users tile

Proposal

As per #454953 (comment 1892918408) we want to add a tile to the top of the AI Impact dashboard with the Code Suggestions Unique Users information.

We will create a new component for this on the frontend as per #454953 (comment 1891405255)

Implementation

• Add single stat tile to the AI Impact dashboard for Unique users
• For the tiles, the date range for the query: Last 30 days (which we can mention in the (i) tooltip)
• Comparison table: (No change)

Note: For tile titles and help text, see: #454953 (closed)

Out of scope

• Trend indicator
• Trendline