contributor count project side panel feature

Problem to Solve

As outlined in Show total contributors numbers on project home... (#259793), a project's homepage does not include the total number of contributors.

Without one, it's a little more challenging to understand how active a project is when you first land on its homepage.

Proposed Solution

Create a small avatar-based contributor count section on the project's home page sidebar that shows the total number of distinct contributors and their commit statistics. Closes #259793

Demo Video

contributor_side_panel_demo

Screenshots

Why Total Contributor Count?

Showing the total number of contributors for any given project has several benefits:

• Allows project newcomers to get a glimpse of the project's popularity and activity.
• Increased analytics adoption: We now have another entry point to link into the analytics features section.
• Incentivizes both community and internal contributions as developers want to "see themselves on the contributors list".
• Incentivizes high contribution counts since the list is ranked by the number of contributions
• Incentivizes open source project creation on gitlab.com with another success metric

Proof of Concept (POC) Implementation Details

See the following MRs for details:

• !214624
• gitaly!8310