feat(openvpn): explain ip route error in logs

- `RTNETLINK answers: File exists` changed to warning with explanation
- `Linux route add command failed:` changed to warning with explanation

internal/openvpn/logs.go

@@ -65,6 +65,16 @@ That error usually happens because either:
 		filtered = s
 		level = levelInfo
 	}
+
+	switch {
+	case filtered == "RTNETLINK answers: File exists":
+		filtered = "OpenVPN tried to add an IP route which already exists (" + filtered + ")"
+		level = levelWarn
+	case strings.HasPrefix(filtered, "Linux route add command failed: "):
+		filtered = "Previous error details: " + filtered
+		level = levelWarn
+	}
+
 	filtered = constants.ColorOpenvpn().Sprintf(filtered)
 	return filtered, level
 }

internal/openvpn/logs_test.go

@@ -43,6 +43,36 @@ func Test_processLogLine(t *testing.T) {
 			"AUTH: Received control message: AUTH_FAILED",
 			"AUTH: Received control message: AUTH_FAILED\n\nYour credentials might be wrong 🤨\n\n",
 			levelError},
+		"TLS key negotiation error": {
+			s: "TLS Error: TLS key negotiation failed to occur within " +
+				"60 seconds (check your network connectivity)",
+			filtered: "TLS Error: TLS key negotiation failed to occur within " +
+				"60 seconds (check your network connectivity)" + `
+🚒🚒🚒🚒🚒🚨🚨🚨🚨🚨🚨🚒🚒🚒🚒🚒
+That error usually happens because either:
+
+1. The VPN server IP address you are trying to connect to is no longer valid 🔌
+   Update your server information using https://github.com/qdm12/gluetun/wiki/Updating-Servers
+
+2. The VPN server crashed 💥, try changing your VPN servers filtering options such as SERVER_REGIONS
+
+3. Your Internet connection is not working 🤯, ensure it works
+
+4. Something else ➡️ https://github.com/qdm12/gluetun/issues/new/choose
+`,
+			level: levelWarn,
+		},
+		"RTNETLINK answers: File exists": {
+			s: "ERROR: RTNETLINK answers: File exists",
+			filtered: "OpenVPN tried to add an IP route which already exists " +
+				"(RTNETLINK answers: File exists)",
+			level: levelWarn,
+		},
+		"Linux route add command failed": {
+			s:        "ERROR: Linux route add command failed: some error",
+			filtered: "Previous error details: Linux route add command failed: some error",
+			level:    levelWarn,
+		},
 	}
 	for name, tc := range tests {
 		tc := tc