Centralized the cache expiration times

Signed-off-by: Ethan Wellenreiter <ewellenreiter@gmail.com>

backend/internal/storage/cache/redis_user.go

@@ -4,9 +4,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
-	"time"
 
-	// auth_storage "git.ewellenr.ca/receipt_indexer/backend/internal/storage/auth"
 	"git.ewellenr.ca/receipt_indexer/backend/internal/storage"
 	"github.com/redis/go-redis/v9"
 )
@@ -15,8 +13,6 @@ type UserStore struct {
 	rdb *redis.Client
 }
 
-const UserExpTime = time.Minute
-
 func (s *UserStore) Get(ctx context.Context, userID int64) (*storage.User, error) {
 	cacheKey := fmt.Sprintf("user-%d", userID)