Task: Create Migration to Update Leaderboard ID Type

[zysim]

Leaderboard's ID was initially set to long, and that fact is included in the initial migration files. As its ID type is now ulong, we'll need to run a second migration that updates its type.

To run a migration via the dotnet CLI:

$ dotnet tool restore # If you haven't installed CLI tools yet
$ dotnet ef migrations --project LeaderboardBackend add -c ApplicationContext UpdateLeaderboardIdType

Affected Functionality

As long as we don't merge in PRs that create new models yet, especially those that have a relationship with Leaderboards, we should be fine.

Other Relevant Issues

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[RageCage64]

Offline discussion lead to this no longer being required. GUIDs are only really important as an identifier for users, not really for anything else.