git-lfs-transfer: Enable in shell and introduce batch download

Following the merging of git-lfs-transfer: Add stub for SSH LFS transfer (!855 - merged), enable the functionality and introduce the first supported command, batched download.

Issue:

• Add support for the new pure SSH-based LFS prot... (gitlab#336618 - closed)
• git-lfs-transfer: Enable in shell and introduce... (#748 - closed)