chore(lint): add musttag linter and fix lint errors

Breaking change: JSON fields changed in the server API

internal/models/servers.go

@@ -11,7 +11,7 @@ import (
 	"github.com/qdm12/gluetun/internal/constants/providers"
 )
 
-type AllServers struct {
+type AllServers struct { //nolint:musttag
 	Version           uint16 // used for migration of the top level scheme
 	ProviderToServers map[string]Servers
 }