Feat: rework Surfshark servers data (#575)

- Feat: `MULTIHOP_ONLY` variable
- Feat: `COUNTRY` variable
- Feat: `CITY` variable
- Feat: `REGION` variable, with retro-compatibility
- Feat: merge servers from API, zip and hardcoded hostnames
- Fix: remove outdated and duplicate servers
- Maint: faster update with fully parallel DNS resolutions

internal/configuration/selection.go

@@ -40,6 +40,9 @@ type ServerSelection struct { //nolint:maligned
 	// VPNUnlimited
 	StreamOnly bool `json:"stream_only"`
 
+	// Surfshark
+	MultiHopOnly bool `json:"multihop_only"`
+
 	OpenVPN   OpenVPNSelection   `json:"openvpn"`
 	Wireguard WireguardSelection `json:"wireguard"`
 }