Import gvisor-tap-vsock/pkg/tcpproxy

Import https://github.com/containers/gvisor-tap-vsock/blob/v0.8.6/pkg/tcpproxy/tcpproxy.go
into `pkg/tcpproxy`.

Changes to the file will be added in follow-up commits.

Fix issue 3685

Signed-off-by: Akihiro Suda <[email protected]>

Author: AkihiroSuda