Migrate away from class-transfomer

This is a rethought version of my previous ticket https://github.com/aws-cloudformation/cloudformation-cli-typescript-plugin/issues/68

To resummarize the issues with `class-transformer`:

* The serialization breaks down in the face of unsupported CloudFormation JSON Schema Features, and increases complexity since JSON Schema features must be manually mapped to the Class Transformer equivalent.
* It ties the implementation to TypeScript's decorators which are soon to be completely deprecated and redesigned entirely, and results in a data model that might be foreign to a lot of JavaScript developers today (outside angular and nestjs)
* Because of the above, it prevents JavaScript from working (though I'd personally always encourage TS over JS) (https://github.com/aws-cloudformation/cloudformation-cli-typescript-plugin/issues/8)
* ~The project isn't also super alive right now: https://github.com/typestack/class-transformer/issues/1272~ Possibly no longer as valid, it looks like the projects might be getting new maintainers.

The updated proposal proposes swapping `class-transformer` with three components:

* The package [camelcase-keys](https://www.npmjs.com/package/camelcase-keys) to handle the CloudFormation-to-JS object key camelcasing.
* The package [AJV](https://www.npmjs.com/package/ajv) to handle validating the incoming event properties, provide friendly(er) error messages, as well as [automatic type conversion](https://ajv.js.org/coercion.html)
* The package [json-schema-to-typescript](https://www.npmjs.com/package/json-schema-to-typescript) to handle consuming the resource definition and outputting type information for a richer experience.

While a very large change, it would uncouple this plugin from TypeScript and an unmaintained library while hopefully simplifying the Dev UX of developing a resource in typescript.

For example, a simple handler like the template default would become (example greatly appreviated):

```typescript
// handlers.ts
import { Resource, TypeConfiguration } from "./.generated/models";
import { createResource, ProgressEvent, exceptions } from '@amazon-web-services-cloudformation/cloudformation-cli-typescript-lib';

const { entrypoint, testEntrypoint } = createResource({
typeName: Resource.TypeName,
schema: Resource.Schema,
// Type information for all the below is automatically infered
async create({ session, properties, request, logger, typeConfiguration }) {
// Example:
try {
const { apiKey } = typeConfiguration;
const response = await fetch(`https://api.someservice.com`, {
method: 'POST',
headers: { 'x-api-key': apiKey },
body: { ...properties },
});
const { id } = await response.json();
properties.id = id;
// else handle error
} catch(err) {
logger.log(err);
// exceptions module lets CloudFormation know the type of failure that occurred
throw new exceptions.InternalFailure(err.message);
// this can also be done by returning a failed progress event
// return ProgressEvent.failed(HandlerErrorCode.InternalFailure, err.message);
}
return properties;
},
/* more handlers.... */
async list({ properties, typeConfiguration }) {
/* ...some list code... */
// Just return a plain array of models, validate via typescript & ajv
return [/* list of plain old javascript models */];
},
});

export { entrypoint, testEntrypoint };

```

This also externalizes a lot of concerns unnecessary to the user code, infers a lot more of type information automatically, and makes developing resource types much less mentally onerous allowing developers to focus on business logic.

It would require more work with the SDK and generated code however.

Prüfe zuerst Issue 68 und das vorgeschlagene handlers.ts-Beispiel, und untersuche anschließend das SDK und den generierten Code, für den laut Issue Änderungen erforderlich wären. Verfolge die aktuelle class-transformer-Integration und identifiziere betroffene Einstiegspunkte, bevor du camelcase-keys, AJV und json-schema-to-typescript bewertest. Die Aufgabe ist abgeschlossen, wenn das Plugin nicht mehr von class-transformer abhängt, den vorgeschlagenen JavaScript- und TypeScript-Workflow unterstützt und die erforderlichen Änderungen am SDK und am generierten Code enthält.

Vom Indexierungsmodell aus dem Issue-Text verfasst.