Add AWSKeyManager implementation

[KendallWeihe]

We currently have a LocalKeyManager implementation for KeyManager but other web5 SDKs have an implementation for AWS KMS

Do we want to add an AWS KMS implementation here in this repo? Or implement the it in a different repo by using the KeyManager interface from this repo?

If we want to implement it in this repo, where will we place it within our code (and therefore which package will it be consumed from)?

• web5-js has a dedicated NPM package for this named crypto-aws-kms (link)
• web5-kt has an AwsKeyManager implementation within its crypto package (link)