Add support for batch download operation

• Drops Accept for all download requests,
• Allows to do batch download for public projects and non-authorized users
• Returns 501 for legacy API with message to upgrade the client

/cc @marin @jacobvosmaer @yorickpeterse

Reassigned to @marin

Current implementation will work if we disable lfs batch (the new API 1.0):

git config lfs.batch false

As for downloading.

It appears that we implement part of the API 0.5 and part of API 1.0:

1. we support downloading only using old API 0.5
2. we support uploading only using a new Batch API

https://github.com/github/git-lfs/blob/7379fa9087b83ebd1f30d0af53320007fe3cc4be/docs/api/http-v1-batch.md

This MR implements missing pieces of API 1.0. I'm also thinking that we should be nice and say to client that your are using legacy unsupported API. It will help us with old clients, saying them exactly what is broken.

Why did you remove this header? According to spec it requires the header. At least for the Content-type.

I don't see how the spec requires that Accept: application/vnd.git-lfs+json; charset=utf-8 is sent to the storage API. I agree with removing this line.

This looks good. As discussed offline with @marin and @ayufan, we should probably drop support for GET /info/lfs to avoid future surprising bugs, and only support POST /info/lfs/batch.

mentioned in issue #3564 (closed)

This is broken since release of git-lfs 1.0.1: https://github.com/github/git-lfs/commit/f56cd54ad7f8e13df6415a568f5681394bd44b31

Added 1 commit:

• 14d95b05 - Part of tests done [ci skip]

Added 1 commit:

• b8d8292b - Fix upload tests, reformat code and make rubocop happy

Added 1 commit:

• dbc0be1b - Error 501 when client is using deprecated API.

Title changed from [WIP] Add support for batch download operation to Add support for batch download operation

mentioned in merge request !1853 (merged)

mentioned in issue #3565 (closed)

mentioned in issue #3416 (closed)

Status changed to merged

mentioned in commit 807c1a99

mentioned in commit b6f0eddc