One commonly requested feature for Git LFS is support for local files.
Currently, we tell users that they must use a standalone transfer
agent, which is true, but nobody has provided one yet. Since writing a
simple transfer agent is not very difficult, let's provide one
ourselves.
Introduce a basic standalone transfer agent, git lfs standalone-file,
that handles uploads and downloads. Add a default configuration required
for it to work, while still allowing users to override this
configuration if they have a preferred implementation that is more
featureful. We provide this as a transfer agent instead of built-in
because it avoids the complexity of adding a different code path to the
main codebase, but also serves as a demonstration of how to write a
standalone transfer agent for others who might want to do so, much
like Git demonstrates remote helpers using its HTTP helper.
