feat(api): add V2 JSON:API relationship endpoint for PlayerAchievementSet resources

[wescopeland]

This PR adds a V2 API relationship endpoint for PlayerAchievementSet resources. This is a follow-up to #4528.

These resources are accessible by two means:

1. Directly by GET /users/{user}/player-achievement-sets.
2. Sideways through GET /users/{user}/player-games?include=playerAchievementSets, which allows per-set breakdowns of the retrieved PlayerGame records.

Things worth noting:

1. There is no standalone index for PlayerAchievementSet resources. These records only make sense in the context of other related or parent records.
2. Results are default sorted by -lastUnlockAt (most recent activity first), mirroring PlayerGameSchema's -lastPlayedAt pattern.
3. The achievementSet and game relationships can be included via ?include=achievementSet or ?include=game.
4. The filter[gameId] param filters to achievement sets for a specific game (it joins through game_achievement_sets).
5. A custom UserScopedHasManyThrough relationship class was needed for the sideways player-games?include=playerAchievementSets.
6. Virtually every field in schema is sortable.

How to test this PR

# Get a paginated list of player achievement sets for a user (50 per page)
curl --request GET \
  --url http://localhost:64000/api/v2/users/Scott/player-achievement-sets \
  --header 'X-API-Key: {redacted}'

# Get player achievement sets with game data included
curl --request GET \
  --url 'http://localhost:64000/api/v2/users/Scott/player-achievement-sets?include=game' \
  --header 'X-API-Key: {redacted}'

# Get player achievement sets with achievement set data included
curl --request GET \
  --url 'http://localhost:64000/api/v2/users/Scott/player-achievement-sets?include=achievementSet' \
  --header 'X-API-Key: {redacted}'

# Filter to a specific game
curl --request GET \
  --url 'http://localhost:64000/api/v2/users/Jamiras/player-achievement-sets?filter[gameId]=11289&include=game' \
  --header 'X-API-Key: {redacted}'

# Include per-set breakdowns on player games
curl --request GET \
  --url 'http://localhost:64000/api/v2/users/Scott/player-games?include=playerAchievementSets' \
  --header 'X-API-Key: {redacted}'

# Apply custom pagination
curl --request GET \
  --url 'http://localhost:64000/api/v2/users/Scott/player-achievement-sets?page[number]=2&page[size]=25' \
  --header 'X-API-Key: {redacted}'