Create a FeatureFlag

### Name of the resource

Other

### Resource name

AWS::AppConfig::FeatureFlag

### Description

It would be extremely useful to define feature flags in Cloudformation, as they are most closely linked at deploy time with the code that references them. Not necessarily to define their on/off state, but to simply define their id, name and description.

In the current workflow, enabling a feature flag means that I first implement it in code. Deploy the code, then separately go to the management console and deploy the feature flag, paying close attention to the naming to that it matches. Being able to deploy the flag as part of my cloudformation deploy would eliminate potential errors.

One issue with this is that the API to add a feature flag is to call `createHostedConfigurationVersion` and passing in all existing feature flags along with the new one, so I'm not sure how the implementation would work.

### Other Details

_No response_

Start by reviewing the AWS::AppConfig::FeatureFlag resource request and the createHostedConfigurationVersion API behavior described in the issue. Determine how a CloudFormation deployment could create the flag while preserving existing feature flags; done means the resource can define the requested flag identity, name, and description without disrupting existing flags.

Written by the indexing model from the issue text.