fix(node-type-registry): BlueprintField uses is_required, not is_not_null

The SQL function construct_blueprint() and metaschema_public.field table
both use is_required for the NOT NULL constraint flag. is_not_null only
exists in the low-level PostgreSQL AST package (ColumnDef parse nodes).

Author: pyramation

graphile/node-type-registry/src/blueprint-types.generated.ts

@@ -654,7 +654,7 @@ export interface BlueprintField {
   /** The PostgreSQL type (e.g., "text", "integer", "boolean", "uuid"). */
   type: string;
   /** Whether the column has a NOT NULL constraint. */
-  is_not_null?: boolean;
+  is_required?: boolean;
   /** SQL default value expression (e.g., "true", "now()"). */
   default_value?: string;
   /** Comment/description for this field. */

graphile/node-type-registry/src/codegen/generate-types.ts

@@ -206,7 +206,7 @@ function buildBlueprintField(): t.ExportNamedDeclaration {
         'The PostgreSQL type (e.g., "text", "integer", "boolean", "uuid").'
       ),
       addJSDoc(
-        optionalProp('is_not_null', t.tsBooleanKeyword()),
+        optionalProp('is_required', t.tsBooleanKeyword()),
         'Whether the column has a NOT NULL constraint.'
       ),
       addJSDoc(