Support `tramp-rpc-deploy-bootstrap-method` of `scp` and `rsync`

The current method of "bootstrapping", i.e. copying updated binaries, uses `ssh` or `sshx`. This is very fragile with tramp with ~MB files. Encoding that much data into compressed base64 and stuffing it down the PTY in a single command often fails for strange reasons likely related to input buffer size. Transferring large files using the `scp` or `rsync` protocols is much faster and more reliable with tramp. It would be great to include those as options (possibly even default).