Create a slash command to view a bounty point leaderboard. #57
Description
Similar to #28 we will need to create a new slash command to view the top 5 users and their current bounty point totals. We will make a new DynamoDB table for this in devil-bot-rust-cdk-stack.ts and Rhett/Json will manually track values in the production table for each user. The reason we cannot yet automate this is because bounty points will not solely come from GitHub issues so we can't just read the project data.