document alias keys usage

refactor kms_key_id doc into the same partial

website/source/docs/builders/amazon-chroot.html.md.erb

@@ -159,11 +159,7 @@ each category, the available configuration keys are alphabetized.
 -   `insecure_skip_tls_verify` (boolean) - This allows skipping TLS
     verification of the AWS EC2 endpoint. The default is `false`.
 
--   `kms_key_id` (string) - ID, alias or ARN of the KMS key to use for boot
-    volume encryption. This only applies to the main `region`, other regions
-    where the AMI will be copied will be encrypted by the default EBS KMS key.
-    For valid formats see *KmsKeyId* in the [AWS API docs -
-    CopyImage](https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_CopyImage.html).
+<%= partial "partials/builders/aws-common-opional-fields" %>
 
 -   `from_scratch` (boolean) - Build a new volume instead of starting from an
     existing AMI root volume snapshot. Default `false`. If `true`, `source_ami`

website/source/docs/builders/amazon-ebs.html.md.erb

@@ -237,11 +237,7 @@ builder.
 -   `force_deregister` (boolean) - Force Packer to first deregister an existing
     AMI if one with the same name already exists. Default `false`.
 
--   `kms_key_id` (string) - ID, alias or ARN of the KMS key to use for boot
-    volume encryption. This only applies to the main `region`, other regions
-    where the AMI will be copied will be encrypted by the default EBS KMS key.
-    For valid formats see *KmsKeyId* in the [AWS API docs -
-    CopyImage](https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_CopyImage.html).
+<%= partial "partials/builders/aws-common-opional-fields" %>
 
 -   `iam_instance_profile` (string) - The name of an [IAM instance
     profile](https://docs.aws.amazon.com/IAM/latest/UserGuide/instance-profiles.html)

website/source/docs/builders/amazon-ebssurrogate.html.md.erb

@@ -230,11 +230,7 @@ builder.
     associated with AMIs, which have been deregistered by `force_deregister`.
     Default `false`.
 
--   `kms_key_id` (string) - ID, alias or ARN of the KMS key to use for boot
-    volume encryption. This only applies to the main `region`, other regions
-    where the AMI will be copied will be encrypted by the default EBS KMS key.
-    For valid formats see *KmsKeyId* in the [AWS API docs -
-    CopyImage](https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_CopyImage.html).
+<%= partial "partials/builders/aws-common-opional-fields" %>
 
 -   `iam_instance_profile` (string) - The name of an [IAM instance
     profile](https://docs.aws.amazon.com/IAM/latest/UserGuide/instance-profiles.html)

website/source/partials/builders/_aws-common-opional-fields.html.md

@@ -0,0 +1,7 @@
+-   `kms_key_id` (string) - ID, alias or ARN of the KMS key to use for boot
+    volume encryption. This only applies to the main `region`, other regions
+    where the AMI will be copied will be encrypted by the default EBS KMS key.
+    For valid formats see *KmsKeyId* in the [AWS API docs -
+    CopyImage](https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_CopyImage.html).
+    This field is validated by Packer, when using an alias, you will have to
+    prefix `kms_key_id` with `alias/`.