AWS::KMS::CustomKeyStore

## 1. Title
#### AWS::KMS:CustomKeyStore

## 2. Scope of request
Connection and creation of KMS Custom Key Store (backed by CloudHSM). Documentation of how to create a Custom Key store can be found [here](https://docs.aws.amazon.com/kms/latest/developerguide/custom-key-store-overview.html)

## 3. Expected behavior
In Create, it should create a custom key store on KMS (backed by CloudHSM), once created allows the connection of its associated [CloudHSM cluster ](https://docs.aws.amazon.com/kms/latest/developerguide/disconnect-keystore.html). Maybe this should be a different CFN resource for connect?

## 4. Suggest specific test cases
Creates a CloudHSM cluster ([feature request](https://github.com/aws-cloudformation/aws-cloudformation-coverage-roadmap/issues/755) to be supported on CFN as well).
Once CloudHSM is created, create a KMS Custom Key passing proper [arguments](https://docs.aws.amazon.com/kms/latest/APIReference/API_CreateCustomKeyStore.html).
Finally once Custom Key Store is created, test the [connection of the Custom Key Store](https://docs.aws.amazon.com/kms/latest/APIReference/API_ConnectCustomKeyStore.html) (again maybe a separate CFN resource?).

## 5. Helpful Links to speed up research and evaluation
[CreateCustomKeyStore](https://docs.aws.amazon.com/kms/latest/APIReference/API_ConnectCustomKeyStore.html)
[ConnectCustomKeyStore](https://docs.aws.amazon.com/kms/latest/APIReference/API_ConnectCustomKeyStore.html)

KMS Documentation about Custom Key Store:
[Documentation](https://docs.aws.amazon.com/kms/latest/developerguide/custom-key-store-overview.html)

## 6. Category (required) - Will help with tagging and be easier to find by other users to +1
Security

## 7. Any additional context (optional)
Currently there is no support for creating a CloudHSM cluster via Cloudformation, neither support for creation of custom key store on KMS.