docs(CreateKeyStore): describe as example

[texastony]

The CreateKeyStore API does not allow users to
configure the backing DDB table with CMK for Server Side Encryption
or Point In Time Recovery (PITR).

But it is also not practical to refactor the method
to be flexible to cover all of the DynamoDB Table creation options.

Instead, we should document the API as both a Utility
and an Example;
if users need more control over table creation,
they should create the table outside of this library,
and use the method to verify it's configuration.