Add dataloaders to GraphQL resolvers

[GV14982]

Add dataloaders to our GraphQL resolvers to improve batching and performance, especially for fields that repeatedly load users or recipes in loops.

Start with the resolvers defined in:

• api/graph/

Good candidates include fields that resolve related users, recipes, revisions, ingredients, and steps, as seen in the GraphQL schema files:

• api/graph/schema/user.graphql
• api/graph/schema/recipe.graphql

Prioritize places where N+1 queries are likely, such as:

• Recipe.author
• RecipeRevision.recipe
• RecipeRevision.ingredients
• RecipeRevision.steps
• User.recipes

See gqlgen dataloader docs: https://gqlgen.com/reference/dataloaders/