updater: refactoring and set DNS server correctly

- Fix CLI operation not setting DNS server
- Fix periodic operation not setting DNS server
- Set DNS address for resolution once at start for both CLI and periodic operation
- Inject resolver to each provider instead of creating it within
- Use resolver settings on every call to `.Resolve` method, instead of passing it to constructor
- Move out minServers check from resolver

internal/provider/vpnunlimited/updater/servers.go

@@ -20,7 +20,8 @@ func (u *Updater) FetchServers(ctx context.Context, minServers int) (
 	}
 
 	hosts := hts.toHostsSlice()
-	hostToIPs, warnings, err := u.presolver.Resolve(ctx, hosts, minServers)
+	resolveSettings := parallelResolverSettings(hosts)
+	hostToIPs, warnings, err := u.presolver.Resolve(ctx, resolveSettings)
 	for _, warning := range warnings {
 		u.warner.Warn(warning)
 	}
@@ -28,15 +29,15 @@ func (u *Updater) FetchServers(ctx context.Context, minServers int) (
 		return nil, err
 	}
 
-	hts.adaptWithIPs(hostToIPs)
-
-	servers = hts.toServersSlice()
-
-	if len(servers) < minServers {
+	if len(hostToIPs) < minServers {
 		return nil, fmt.Errorf("%w: %d and expected at least %d",
 			common.ErrNotEnoughServers, len(servers), minServers)
 	}
 
+	hts.adaptWithIPs(hostToIPs)
+
+	servers = hts.toServersSlice()
+
 	sort.Sort(models.SortableServers(servers))
 
 	return servers, nil