Resource not found if there are multiple `cdk.out/*.template.json` files

Heya. 👋🙂 This seems like an interesting project.

I was taking it for a spin, but unfortunately failed to put it to any use:

```
$ AWS_REGION=… AWS_PROFILE=… npx cdk-app-cli LambdaFn visit-console
Refreshing stack metadata...
[cdk-app] Error: Could not find resource with aws:cdk:path metadata "…/LambdaFn/Resource" in the CloudFormation template.
````

I read through the source code and came across this:

https://github.com/cdklabs/cdk-app-cli/blob/515c07452588ef5c7b3de66ca2972087c370e426/src/app.ts#L82-L95

It just picks the first `*.template.json` file found.

Checking my `cdk.out` directory, I found there are 15 `*.template.json` files and I suspect this is what makes the above command fail for me (and probably for most CDK apps generating multiple templates).

The `TODO` comment in the code somewhat suggests this is a known issue.

Are there any plans to address this?

Thanks a bunch. 🙇

I wish you a great day. ☀️
Paul