First implementation of fetching collections of book managed by user

internal/model/collection.go

@@ -0,0 +1,11 @@
+package model
+
+import "gorm.io/gorm"
+
+type Collection struct {
+	gorm.Model
+	Name   string
+	User   User
+	UserID uint
+	Books  []Book `gorm:"many2many:collection_books;"`
+}