Add a new attribute to the deployment resource that allows the user to get a stream with the deployment content attached to the response, a la what we do with the subsystem=logging/log-file=* resource's "stream" attribute.

The attribute must be configured as runtime-only and read-only.

The read handler that handles the attribute should only attach a stream if the following conditions are met, otherwise the value for the attribute should remain as 'undefined'.

1) The resource's "content" attribute has only a single element in the list. (This is always the case today; adding a check for this is just future proofing)

2) The first element in the "content" attribute list has a defined value in its "hash" field. (This confirms the content is stored in the content repo. We won't support serving unmanaged content as we have insufficient control over it.)

3) The first element in the "content" attribute list has a 'true' as value of its "archive" field. (Current this will always be the case; this is future proofing for when we add support for exploded content in the content repo. Trying to assemble a stream from exploded content is currently out of scope for this feature.)