Create copy usernames button on hackathon leaderboard

Why

The old leaderboard had a function to copy usernames in order to award swag via the Rewards page of the contributors platform. This issue is to implement that functionality for the hackathon leaderboard at https://contributors.gitlab.com/hackathon.

Implementation plan

• Add a simple way to copy usernames from the hackathon leaderboard (perhaps a keyboard shortcut as this is just for us to use as admins... or maybe a button in the username header cell of the tabl?e maybe using the "copy to clipboard glypth"
• Only users with a score above 0 should be copied
• The format should be usernames without the @, one username per line like

user1
user2
user3
user4

/cc @gitlab-org/developer-relations/contributor-success