Allow pipe in data in CLI mode

[deajan]

See N.L

[deajan]

So restic totally supports this via https://restic.readthedocs.io/en/latest/040_backup.html#reading-data-from-stdin

We need to find a way to redirect stdin to restic without the need of queues or additionnal python plumbing, to avoid memory copies.
command_runner allows giving a subprocess a stdin pipe. Let's see if we can pass a fd (sys.stdin). If so, we need to handle:

• encoding to use none (bytes), which will affect restic stdout stderr which will need later stage encoding
• buffering to use standard expected buffers, or even bigger ones since restic deals in generally bigger than 64k chunks (need performance tests)

[deajan]

Basically implemented, we still need to test this in compiled version in both windows and linux.

[deajan]

Tested on Linux and Windows platforms, both compiled and interpreted versions.