Add AWS AppConfig Feature Flags Provider

[Arthur1]

Proposal

AWS AppConfig is an AWS managed service that manages application configuration. I believe that AppConfig's Feature Flags could be one of the options for OpenFeature backend.

My proposal is to implement the provider for AppConfig Feature Flags in the Go SDK. This provider communicates with the AppConfig Agent to evaluate Feature Flags.

Please let me know if you need additional information.

Contribution

I already have the implementation of provider for AppConfig Feature Flags.

https://github.com/Arthur1/openfeature-provider-go-aws-appconfig/

I can move this implementation under openfeature/go-sdk-contrib repository if the community wants.