Wireguard support for Mullvad and Windscribe (#565)

- `internal/wireguard` client package with unit tests
- Implementation works with kernel space or user space if unavailable
- `WIREGUARD_PRIVATE_KEY`
- `WIREGUARD_ADDRESS`
- `WIREGUARD_PRESHARED_KEY`
- `WIREGUARD_PORT`
- `internal/netlink` package used by `internal/wireguard`

.devcontainer/Dockerfile

@@ -1 +1,2 @@
 FROM qmcgaw/godevcontainer
+RUN apk add wireguard-tools

.devcontainer/docker-compose.yml

@@ -4,6 +4,8 @@ services:
   vscode:
     build: .
     image: godevcontainer
+    devices:
+      - /dev/net/tun:/dev/net/tun
     volumes:
       - ../:/workspace
       # Docker socket to access Docker server
@@ -23,7 +25,8 @@ services:
       - TZ=
     cap_add:
       # For debugging with dlv
-      - SYS_PTRACE
+      # - SYS_PTRACE
+      - NET_ADMIN
     security_opt:
       # For debugging with dlv
       - seccomp:unconfined