support piping data into aws kms encrypt commands

Currently you cannot pipe ( | ) into the kms encrypt. Given that most of the data being encrypted is sensitive, it might be nice not write it to disk, especially if it is a generated token etc.

There is a work around

``aws kms encrypt --key-id xxxxx-xxxx-xxxx-xxxxx-xxxxxxx --output text --plaintext `jwtgen -a HS256 -s xyzw -c key1=value1` --query CiphertextBlob``

the ` on linux wraps the jwtgen command here. For Windows this wouldn't be possible. On linux kind of annoying to type it out this way as its hard to test, etc.