Add gocritic linter (#1324)

* Add gocritic linter

`gocritic` provides diagnostics that check for bugs, performance, and style issues

We disable the following checks:

- commentFormatting
- captLocal
- deprecatedComment

This PR contains many `//nolint:gocritic` to disable `appendAssign`.

iface/wg_configurer_nonandroid.go

@@ -141,7 +141,7 @@ func (c *wGConfigurer) removeAllowedIP(peerKey string, allowedIP string) error {
 
 	for i, existingAllowedIP := range existingPeer.AllowedIPs {
 		if existingAllowedIP.String() == ipNet.String() {
-			newAllowedIPs = append(existingPeer.AllowedIPs[:i], existingPeer.AllowedIPs[i+1:]...)
+			newAllowedIPs = append(existingPeer.AllowedIPs[:i], existingPeer.AllowedIPs[i+1:]...) //nolint:gocritic
 			break
 		}
 	}