add KMSEncryptPolicy policy template

[jlhood]

Description:

SAM policy templates has a KMSDecryptPolicy, but no KMSEncryptPolicy that allows kms:Encrypt action. This issue is to add a KMSEncryptPolicy that is almost identical to KMSDecryptPolicy, but has kms:Encrypt action instead of kms:Decrypt action. Should be a simple update. Here's an example of a past PR that added a new policy template for reference: #904

[john-aws]

Is this policy actually useful as written? It can't be used to publish KMS-encrypted data to an SNS topic, for example, because KMSEncryptPolicy doesn't include kms:GenerateDataKey.