[New resource] Import Public Key Material into Key Pair

It would be nice to be able to import a key pair into a region using Cloud Formation.

It is already possible to do this in the AWS console, and you can do this using the AWS CLI:

`aws ec2 import-key-pair --key-name default-bastion-key --public-key-material ""`

I know it is possible to reference key pair names that already exist in cloud formation template parameters like this:

```
BastionKey:
Description: Name of an key pair for SSH access to the Bastion Host
Type: "AWS::EC2::KeyPair::KeyName"
Default: default-bastion-key
```

... and then use the KeyName in the property of an instance.

It would be great if importing the public key was possible using CloudFormation templates.

Start by reviewing the CloudFormation template parameter and EC2 KeyName examples in the issue, then compare the requested behavior with the AWS CLI import-key-pair operation. Done means a CloudFormation template can provide public key material, import it into a region, and use the resulting key pair for an instance.

Written by the indexing model from the issue text.