Fix docs for the volume parameter in the ec2_instance module (#42710)

The existing docs specified valid keys of ebs.device_type and ebs.device_size
but they should instead be ebs.volume_type and ebs.volume_size.

lib/ansible/modules/cloud/amazon/ec2_instance.py

@@ -108,7 +108,7 @@ options:
   volumes:
     description:
     - A list of block device mappings, by default this will always use the AMI root device so the volumes option is primarily for adding more storage.
-    - A mapping contains the (optional) keys device_name, virtual_name, ebs.device_type, ebs.device_size, ebs.kms_key_id,
+    - A mapping contains the (optional) keys device_name, virtual_name, ebs.volume_type, ebs.volume_size, ebs.kms_key_id,
       ebs.iops, and ebs.delete_on_termination.
     - For more information about each parameter, see U(https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_BlockDeviceMapping.html)
   launch_template: