Add support for UpdateShardCount

[theladyjaye]

https://docs.aws.amazon.com/kinesis/latest/APIReference/API_UpdateShardCount.html

It doesn't have to do anything, just respond generically not actually implement any sharding increases or decreases.

This library is a part of Localstack which mocks AWS services. When using Localstack with Terraform, Terraform will call UpdateShardCount

[Sytten]

Is there any plan to support that, resharding is very hard and testing it would be useful.

[sdabhi23]

@mhart I would be happy to take this up and implement properly. There have been 2 previous attempts, I can build on top of them.

ref: #48, #103