examples/vweb_fullstack: fix wrong db ORM-fields (#17907)

Author: l-33ter

examples/vweb_fullstack/src/auth_dto.v

@@ -1,6 +1,6 @@
 module main
 
 struct AuthRequestDto {
-	username string [required]
-	password string [required]
+	username string [nonull]
+	password string [nonull]
 }

examples/vweb_fullstack/src/product_entities.v

@@ -4,6 +4,6 @@ module main
 struct Product {
 	id         int    [primary; sql: serial]
 	user_id    int
-	name       string [required; sql_type: 'TEXT']
+	name       string [nonull; sql_type: 'TEXT']
 	created_at string [default: 'CURRENT_TIMESTAMP']
 }

examples/vweb_fullstack/src/user_entities.v

@@ -4,8 +4,8 @@ module main
 pub struct User {
 mut:
 	id       int       [primary; sql: serial]
-	username string    [required; sql_type: 'TEXT'; unique]
-	password string    [required; sql_type: 'TEXT']
+	username string    [nonull; sql_type: 'TEXT'; unique]
+	password string    [nonull; sql_type: 'TEXT']
 	active   bool
 	products []Product [fkey: 'user_id']
 }