Add linters and fix lint issues

internal/settings/openvpn_test.go

@@ -19,6 +19,7 @@ func Test_OpenVPN_JSON(t *testing.T) {
 	}
 	data, err := json.Marshal(in)
 	require.NoError(t, err)
+	//nolint:lll
 	assert.Equal(t, `{"user":"","verbosity":0,"runAsRoot":true,"cipher":"","auth":"","provider":{"name":"name","serverSelection":{"networkProtocol":"","regions":null,"group":"","countries":null,"cities":null,"isps":null,"owned":false,"customPort":0,"numbers":null,"encryptionPreset":""},"extraConfig":{"encryptionPreset":"","openvpnIPv6":false},"portForwarding":{"enabled":false,"filepath":""}}}`, string(data))
 	var out OpenVPN
 	err = json.Unmarshal(data, &out)