lfs: add the 'Authorization' property to the Batch API response, if present
The client copies all of these properties under 'header' to the HTTP Headers of
the subsequent GET or PUT request that it performs. That allows the Basic HTTP
authentication used to authorize the Batch API request to also authorize the
upload/download action.
There's likely further work to do here. There's an 'authenticated' boolean key
in the Batch API response that can be set, and there is an 'LFS-Authenticate'
header that is used instead of 'WWW-Authenticate'[1]. (We likely need to
support both, since some hosting solutions are likely to only respond with the
latter.) In any event, this works with SCM Manager, so there is real world
benefit.
I'm limiting the headers returned to 'Basic', because that's all the lfs spec
calls out. In practice, I've seen gitbucket emit custom header content[2].
[1] https://github.com/git-lfs/git-lfs/blob/master/docs/api/batch.md#response-errors
[2] https://github.com/gitbucket/gitbucket/blob/
35655f33c7713f08515ed640ece0948acd6d6168/src/main/scala/gitbucket/core/servlet/GitRepositoryServlet.scala#L119