bug: setting the prompted architectures generates an error

## Issue

I am running `SAM CLI, version 1.36.0` and when I try to input the `architectures` prompted by Cookiecutter I get an `Error: Unable to decode to JSON.` error. And this might not be intuitive for a first time user

```text
sam init --location cookiecutter-aws-sam-eventbridge-hello-java-gradle
project_name [Your EventBridge Starter app]: x
runtime [java11]:
architectures [default]: arm64
Error: Unable to decode to JSON.
```

## Work around

If I set the input to `{"value":["arm64"]}` for `architectures` then this works.

```text
sam init --location cookiecutter-aws-sam-eventbridge-hello-java-gradle
project_name [Your EventBridge Starter app]: x
runtime [java11]:
architectures [default]: {"value":["arm64"]}
```

Or if I pass in `architecture` in the cli and not enter anything in `architectures`:

```script
sam init --location java11/cookiecutter-aws-sam-eventbridge-hello-java-gradle --architecture arm64
```

## Possible Solution

- Change the `architectures` in `cookiecutter.json` to be a simple string value like `runtime`, this would mean change all of the templates and CLI

Reproduce the failure with `sam init --location cookiecutter-aws-sam-eventbridge-hello-java-gradle` and the `architectures` value `arm64`. Start by inspecting the affected `cookiecutter.json` and the architecture handling in the CLI, then review the other templates mentioned by the proposed solution. Done means a plain `arm64` prompt works without breaking the documented JSON form or CLI option.

Written by the indexing model from the issue text.