feat: start adding leaderboard service

[ZakShearman]

Aims of the leaderboard service:

• Personal leaderboard, view your top x scores
• Variable time periods, e.g. 1d, 7d, 1month, lifetime
• Filtering for players (e.g. friends leaderboard)

Leaderboards must be pre-configured in YAML so we don't store too much data (e.g. we need to specify a personal leaderboard with a limit of X scores so we don't store them all). Direction (ASC, DESC) also needs to be specified.

The aim is that a server can push a score and the leaderboard service will store it if it deems necessary (based on config). It will store playerID, leaderboardID, score which will allow us to filter however we want.

Currently unsure how configuration can be done. We can easily create and query a leaderboard dynamically as we can just shove them all in one MongoDB collection.

Other DoD:

• proto-specs has been updated
• Leaderboard updates are published to Kafka
• MongoDB indexes are created
• Method to delete an entry from a leaderboard (by entry ID and position index)

Current Design Considerations:

• Q: Should scores be pushed to leaderboards via Kafka or gRPC
  • A: Can do Kafka, update results (if any changes to leading) will have to be pushed async via a return Kafka message