chore(spec2cdk): support local, temporary service files

To work with new features that are not released on CFN yet, we need the ability to provide local schema overrides.
This changes adds support for this, by importing additional schema files into the model database before codegen.

tools/@aws-cdk/spec2cdk/README.md

@@ -37,6 +37,11 @@ Path patterns can use the following variables:
 
 ```
 
+## Temporary Schemas
+
+You can import additional, temporary CloudFormation Registry Schemas to test new functionality that is not yet published in `@aws-cdk/aws-service-spec`.
+To do this, drop the schema file into `temporary-schemas/us-east-1` and it will be imported on top of the default model.
+
 ## Use as @aws-cdk/cfn2ts replacement
 
 You can use the `cfn2ts` binary as a drop-in replacement for the existing `@aws-cdk/cfn2ts` command.

tools/@aws-cdk/spec2cdk/lib/generate.ts

@@ -1,5 +1,6 @@
 import * as path from 'path';
 import { loadAwsServiceSpec } from '@aws-cdk/aws-service-spec';
+import { DatabaseBuilder } from '@aws-cdk/service-spec-importers';
 import { SpecDatabase } from '@aws-cdk/service-spec-types';
 import { TypeScriptRenderer } from '@cdklabs/typewriter';
 import * as fs from 'fs-extra';
@@ -118,6 +119,12 @@ export interface GenerateOutput {
 export async function generate(modules: GenerateModuleMap, options: GenerateOptions) {
   enableDebug(options);
   const db = await loadAwsServiceSpec();
+
+  // Load additional schema files
+  await new DatabaseBuilder(db as any, { validate: false })
+    .importCloudFormationRegistryResources(path.join(__dirname, '..', 'temporary-schemas'))
+    .build();
+
   return generator(db, modules, options);
 }