feat(api): add V2 JSON:API relationship endpoint for user leaderboard entries

[wescopeland]

Accompanies #5043.

This PR adds a user-scoped leaderboard entries relationship endpoint that supports a gameId filter. This is intended to allow clean migration from API_GetUserGameLeaderboards.

GET /api/v2/users/{user}/leaderboard-entries
GET /api/v2/users/{user}/leaderboard-entries?filter[gameId]=1,2,3
GET api/v2/users/{user}/leaderboard-entries?include=leaderboard.games

Things worth noting:

1. Each entry's rank is computed with a correlated subquery mirroring V1's calculated_rank, since a user's entries span many leaderboards. The subquery leans on the index added in chore: add (leaderboard_id, deleted_at, score) index to leaderboard_entries #5043.
2. The subquery excludes untracked users in rank calculations.
3. GETs against untracked users ({user}) return an empty list.
4. Hidden leaderboards, hub/event games, and soft-deleted leaderboards/entries are excluded, consistent with /leaderboards/{id}/entries.
5. filter[gameId] is comma-delimited.
6. Default sort is leaderboard ID ascending.
7. ?include=leaderboard.games is allowed for tying entries back to games. Include paths are listed explicitly rather than via maxDepth: 2. The plural games is intentional and matches the existing leaderboards resource - anticipating that leaderboards can potentially be attached to multiple games/sets per leaderboard ID.

[greptile-apps]

Confidence Score: 5/5

This looks safe to merge.

• No blocking issues found in the changed code.

_{Reviews (3): Last reviewed commit: "Merge branch 'master' into v2-user-lb-en..." | Re-trigger Greptile}

[Jamiras]

Possibly mentioned in previous PR, but is there any value in exposing the created_at field? The updated_at should reflect the last submitted time, but does the first submitted time matter, especially given that we don't have the first submitted value (or anything in-between)?

[wescopeland]

I lean towards keeping it here, as it can still be kinda meaningful. Even without the submission history, created_at (obviously) signifies the user's first submitted entry, and it can be compared against updated_at to see the difference between the player's first and best score.

[Jamiras]

Definitely not something I expect implemented right now, but any plans for a filter on rank? i.e. only show leaderboards where the user is # 1 or in the top ten.

[wescopeland]

Seems like a good idea to me.

We could do something like:

• filter[rank]
• filter[maxRank]

I'll track this in my notes.